Solutions for Leetcode

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Problems & Solutions

tags: matma, try also, cool python, cool c++, no number, tricky, string play, good practise in code base grep for 'cool read'

#	Title	Solution	Comments
1	Two Sum	C++	hash map, two pointers. Note that this is a special case (exactly one solution exists). So hash map works fine. In a general case sort + two pointers would work.
2	Add Two Numbers	C++	classic linked list
3	Longest Substring Without Repeating Characters	C++	sliding window
4	Median Of Two Sorted Arrays	C++	can just merge the arrays, try also other solution which is tricky
7	Reverse Integer	C++	as title
8	String To Integer	C C++ Python	as title
10	Regular Expression Matching	Python	check if s matches p, special chars * and . recursion, try also dp
13	Roman To Integer	Python	convert roman number to integer, use hash map
14	Longest Common Prefix	C++	as title, get loops right
15	3Sum	C++	array of ints, find all unique triplets that sum to 0
17	Letter Combinations Of A Phone Number	Python	cartesian product problem
18	4Sum	Python	array of ints, find all unique quadruplets that sum to given target, used set to avoid duplicate quadruplets
20	Valid Parentheses	C Python	classic. stack. also assembly.
22	Generate Parentheses	Python	generate all valid combinations, recursion
23	Merge K Sorted Lists	C++	as title, use priority queue
24	Swap Nodes In Pairs	C++	swap nodes in linked list, play with pointers, good practise
25	Reverse Nodes In K-Group	C++	linked list classic, can use recursion or an extra array
28	Implement strStr()	C	check if s1 is a substring of s2
29	Divide Two Integers	C++	as title, trick with bits
30	Substring With Concatenation Of All Words	C++	within a string s find all concatenations of given set of strings of same size, two hash maps, try also sliding window
31	Next Permutation	Python
33	Search In Rotated Sorted Array	C++	binary search
34	Find First And Last Position Of Element In Sorted Array	Python	self descriptive, use bs
37	Sudoku Solver	Python	backtracking
39	Combination Sum	Python	given int array find combinations that sum up to target, unbound knapsack problem
40	Combination Sum II	Python	Given array of ints and target, find all unique combinations that sum to target. Each number in candidates may only be used once in the combination. Used tuple, try also without tuple.
41	First Missing Positive	Python	move values around i.e. '1' to index 0, '5' to index '6' etc
42	Trapping Rain Water	Python	classic, try also one pass solution
45	Jump Game II	C++	same as 55 but here need to find out min number of jumps
46	Permutations	C++ Python	generate permutations, cool python
47	Permutations II	Python	generate permutations, input might contain duplicates
48	Rotate Image	Python	2d matrix rotate by 90 degrees. just come up with an index convention
49	Group Anagrams	Python	sort + hash, string play
50	Pow(x,n)	Python
51	N-Queens	Python	classic n queens problem, backtracking
53	Maximum Subarray	C++	find the contiguous subarray which has the largest sum. Kadane algo.
54	Spiral Matrix	Python	my solution with O(N) space, try also O(1) space
55	Jump Game	Python	array of ints, each value max jump you can do from the current index, can you reach the last index
60	Permutation Sequence	C++ Python	basically directly find nth permutation
61	Rotate List	C++	rotate linked list by k places
62	Unique Paths	C++	dp
63	Unique Paths II	C++	dp
69	Sqrt(x)	Python	bs, try also Newton
70	Climbing Stairs	Python	Need to reach nth step. Can climb 1 or 2 steps at a time. What's the number of ways to do it. Fibonacci
73	Set Matrix Zeroes	C++ Python	if 0 found, fill whole row and column with 0s. use only constant memory.
74	Search A 2D Matrix	Python	bs and mapping
75	Sort Colors	C++ Python	dutch partitioning problem, sort 3 colors in 1 pass with constant extra space
76	Minimum Window Substring	C++	two strings s and t, return the minimum window substring of s such that every character in t (including duplicates) is included in the window. sliding window.
78	Subsets	C++ Python	get all the subsets, bitmasks or recursion
79	Word Search	Python	check if word is in a grid, dfs
84	Largest Rectangle In Histogram	Python C++	classic stack
91	Decode Ways	Python	string with digits given, mapping is 'a' -> 1, 'b' -> 2, ... 'z' -> 26, return number of ways to decode the string, dp
93	Restore IP Addresses	Python	string with digits, return all possible ips that can be created by adding dots, backtracking
94	Binary Tree Inorder Traversal	Python	iterative solutions
95	Unique Binary Search Trees II	C++ Python	given int n, return all structuraly unique bst trees with values 1 to n, similar to 96
96	Unique Binary Search Trees	Python	how many structurally unique BSTs can you build
97	Interleaving String	C++ Python	check if s3 can be created by interleaving s1 and s2. dp
98	Validate Binary Search Tree	Python	as title, dfs
99	Recover Binary Search Tree	JS	find two swapped nodes in BST. in-order traversal
101	Symmetric Tree	C++ Python	recursive and iterative
102	Binary Tree Level Order Traversal	C++ Python	bfs or pre-order traversal
104	Maximum Depth Of Binary Tree	Python	as title
105	Construct Binary Tree From Preorder And Inorder Traversal	C++	as title
113	Path Sum II	C++ Python	return all root-to-leaf paths where the sum equals targetSum. dfs or bfs
114	Flatten Binary Tree To Linked List	C++ Python	as title
115	Distinct Subsequences	Python	two strings s and t, return the number of distinct subsequences of s which equals t, dp
116	Populating Next Right Pointers In Each Node	C++ Python	as title
118	Pascals Triangle	Python
121	Best Time To Buy And Sell Stock	C
122	Best Time To Buy And Sell Stock II	C++	at each step if profit can be made - do it
123	Best Time To Buy And Sell Stock III	C++ Python	2 transactions allowed, my solution with 2 arrays
124	Binary Tree Maximum Path Sum	Python	recursion
125	Valid Palindrome	C++	classic
127	Word Ladder	C++ Python	bidirectional bfs
128	Longest Consecutive Sequence	C++ Python	given unsorted array find the longest consecutive sequence (if the array was sorted)
131	Palindrome Partitioning	C++ Python	string s, partition s such that every substring of the partition is a palindrome. Return all possible palindrome partitioning of s. dp
133	Clone Graph	C++	use recursion and hash map. grafy
134	Gas Station	C++	visiting a sequence of gas stations, where to start to complete the journey, greedy
136	Single Number	C++	classic xor
137	Single Number II	C++	traverse, keep adding bits on every position, divide modulo by three and voila
138	Copy List with Random Pointer	C++ Python	linked list, each node has an extra random pointer, make deep copy. Recursion or play with pointers and intertwine nodes
139	Word Break	C++	dp
140	Word Break II	Python	dp
141	Linked List Cycle	C++	classic, two pointers
142	Linked List Cycle II	C++	Floyd's Tortoise and Hare cycle detection Algorithm
144	Binary Tree Preorder Traversal	Python	just Inorder Traversal a bit modified
145	Binary Tree Postorder Traversal	C++	iterative solution
146	LRU Cache	C++
150	Evaluate Reverse Polish Notation	C++ Python	classic stack, cool c++ lambda
151	Reverse Words In A String	C++ C
153	Find Minimum In Rotated Sorted Array	C++	as title. bs
154	Find Minimum In Rotated Sorted Array II	C++	duplicates allowed. bs
155	Min Stack	C++	classic, with a trick we can use just one stack
169	Majority Element	C++	Boyer–Moore majority vote algorithm
173	Binary Search Tree Iterator	C++ Python	generator in python
174	Dungeon Game	C++ Python	traverse grid, in each square you either gain or lose energy. what's the minimum start energy to finish. dp
179	Largest Number	C++ Python	array of non-negative ints give. Arrange themm so that they form largest number possible. Need a clever comparison operator
188	Best Time To Buy And Sell Stock IV	C++ Python	k transactions allowed
189	Rotate Array	C++
190	Reverse Bits	C++	O(N) and O(1) solutions
191	Number Of1 Bits	C++	find number of bits set to '1' in a given var, solution in O(N) N - number of '1's
198	House Robber	C++
199	Binary Tree Right Side View	C++ Python	dfs preorder traversal or bfs
200	Number Of Islands	C++	count islands in a binary matrix
204	Count Primes	Python	Eratosthenes sieve
205	Isomorphic Strings	C++ Python	hash, string play
207	Course Schedule	Python	dfs
208	Implement Trie (Prefix Tree)	C++	trie
209	Minimum Size Subarray Sum	C++	as title. similar to 862 but easier
210	Course Schedule II	C++	topological sort
213	House Robber II	Python	like a classic house robber but houses arranged in circle
216	Combination Sum III	Python	Find all valid combinations of k numbers that sum up to n. Only nums 1-9 can be used, and each num used at most once.
218	The Skyline Problem	Python	each building given as [leftX, rightX, height], return a set of points defining the skyline. use edges and heap
221	Maximal Square	Python	binary matrix with 0's and 1's, find largest square made of 1's. use dp.
224	Basic Calculator	Python	add, deduct and parenthesis
226	Invert Binary Tree	C++
227	Basic Calculator II	C++ Python	add, deduct, multiply and divide, cool C++
229	Majority Element II	Python	Boyer–Moore majority vote algorithm
230	Kth Smallest Element in a BST	Python	do in-order traversal while counting
232	Implement Queue Using Stacks	C++	use one stack for input and one for output
236	Lowest Common Ancestor Of A Binary Tree	C++ Python	as title, collect full paths to both nodes first and then easy solve, can be done easier
238	Product Of Array Except Self	C++	int array 'a' given, create a new array 'b' where b[i] = a[0] * a[1] * ... * a[i-1] * a[i+1] * ... * a[sz-1]
239	Sliding Window Maximum	C++ Python	sliding window moving through an array, for each position find a median. multiset or heap or ind of monotonic deque
258	Add Digits	C++ Python	given int num, repeatedly add all its digits until the result has only one digit. can solve it by iteration, also solution in O(1) called digital root
260	Single Number III	C++	in array all elements appear twice except two that appear once. find them. xor all, finda set bit and then extra pass to divide into 2 groups
263	Ugly Number	C++	ugly number is a int whose prime factors are 2, 3, and 5.
264	Ugly Number II	C++ Python	find nth ugly number (that divides only by 2 3 and 5), dp
268	Missing Number	C++	classic xor
273	Integer To English Words	Python	classic, recursion, try also word to integer
274	H-Index	C++ Python	definition of index h - if h of n papers have at least h citations each, and the other n − h papers have no more than h citations each.
283	Move Zeroes	C++	in the array move all 0s to the end
287	Find The Duplicate Number	C++ Python	array has n+1 elements and values between 1 and n (inclusive). Find repeating element using only const space and not modifying the array. bits and marking, try also Floyd's cycle detection
289	Game Of Life	C++	Cellular automaton. The values in the grid are only '0' and '1' so to solve it can just use other bits
290	Word Pattern	C++	similar to isomorphic. hash map.
292	Nim Game	Python	heap of stones, players can remove 1,2, or 3. To win, you need to take the last stone
295	Find Median From Data Stream	C++	two heaps and keep them balanced
297	Serialize And Deserialize Binary Tree	Python C++	pre-order traversal works, not sure about formal proof, easy to see that post and in-order traversals not up to the task
300	Longest Increasing Subsequence	C++ Python	C++ solution easy dp in O(N^2), Python a bit tricky in O(NlnN), matma
309	Best Time To Buy And Sell Stock With Cooldown	Python C++
312	Burst Balloons	Python	burst ballons one by one, each time get score depending on neighbours, what's the max. dp
313	Super Ugly Number	C++ Python	given int n and list of primes, find nth ugly number. dp or heap
315	Count Of Smaller Numbers After Self	C++ Python	merge sort solution
319	Bulb Switcher	Python	bulbs go on and off, figure out the pattern, matma
322	Coin Change	C++	classic dp, the fewest number of coins to make up the amount
324	Wiggle Sort II	C++	Given an int array nums, reorder it such that nums[0] < nums[1] > nums[2] < nums[3]....
326	Power Of Three	C++	check if a given int is a power of 3
327	Count Of Range Sum	Python	Given an int array and two ints lower and upper, return the number of range sums that lie in [lower, upper] inclusive. Prefix sum + merge sort
328	Odd Even Linked List	Python	rearrange nodes in list
329	Longest Increasing Path In A Matrix	Python	dfs with memiozation, try also topological sort
332	Reconstruct Itinerary	C++ Python	given a list of tickets reconstruct an itinerary. Eulerian path. Greedy dfs, build path backwards
334	Increasing Triplet Subsequence	Python
337	House Robber III	C++	house robber in a binary tree
338	Counting Bits	C++	for a sequence of ints e.g 1,2,3,4,5 calculate mapping int - number of bits in binary representation
342	Power Of Four	C++	check if given int is a power of 4, play with bits
345	Reverse Vowels Of A String	C++ Python	as title. good practise.
347	Top K Frequent Elements	C++	as title. heap or bucket sort
348	Shuffle An Array	C++	Fisher Yates Algorithm for random shuffling
354	Russian Doll Envelopes	C++	kind of matryoshka problem with 2d envelopes. sort and then dp
371	Sum Of Two Integers	C++	as title. bits manipulation.
375	Guess Number Higher Or Lower II	C++	kind of minimax with transposition table/memoization
380	Insert Delete Get Random in O(1)	C++	class to insert values, delete and get random
394	Decode String	Python	string encoded with ints, brackets and chars. use stack.
395	Longest Substring With At Least K Repeating Characters	C++	string s and int k, return length of longest substring such that the frequency of each char in substring is greater than or equal to k. divide and conquer.
396	Rotate Function	Python	given array rotate it and calculate sum = arr0 * 0 + arr1 * 1 + ... , what rotation gives the biggest sum
402	Remove K Digits	C++	for a given int remove K digits to get min value, greedy
403	Frog Jump	Python	array of ints gives mapping index to position, frog jumping, dp
406	Queue Reconstruction By Height	C++ Python	array of pairs (person's height, person's position in the original queue) given. Reconstruct the queue based on the array.
407	Trapping Rain Water II	C++	classic in 3D. bfs with heap
413	Arithmetic Slices	Python	Gauss formula
416	Partition Equal Subset Sum	Python	can split array into two that have same sum, dp knapsack problem
417	Pacific Atlantic Water Flow	C++	grid borders ocean A and ocean P. Values represent height. Find squares from which water can flow to both Oceans. bfs
419	Battleships In A Board	C++	2d board has 1d ships. Count them in one pass without modifying the board and using O(1) extra space. identify upper left corners of ships
424	Longest Repeating Character Replacement	C++	similar to Max Consecutive Ones, sliding window
437	Path Sum III	C++	in a binary tree find number of paths that sum to target, similar to Subarray Sum Equals K, hash map
438	Find All Anagrams In A String	C++	2 strings,get all indices of p anagrams in s.sliding window
442	Find All Duplicates In An Array	C++	array of size n has values 1-n. some appear once and some twice. find duplicates. Cyclic sort
445	Add Two Numbers II	C++	reverse linked list
450	Delete Node In A BST	C++ Python	dfs, find the node, if it has only left child - its easy, if it has both - find min value in the right child branch then easy
451	Sort Characters By Frequency	Python
453	Minimum Number Of Arrows To Burst Balloons	Python	sort and greedy
460	LFU Cache	C++ Python	C++ solution optimal, Python stuff my more naive implementation
462	Minimum Moves To Equal Array Elements II	Python	in a move we can add or subtract 1 from an array element. min moves to make elements equal. matma.
464	Can I Win	C++	game in which players alternate and take numbers from pool until a certain sum is reached, minimax with tt
474	Ones And Zeroes	C++ Python	given a set of binary strings. Pick as many as you can constraint being you end up with max total number of 0s m and 1s n, knapsack kind of in 2d, dp
480	Sliding Window Median	C++	sliding window moving through an array, for each position find a maximum. multiset and try also 2 heaps
493	Reverse Pairs	C++	merge sort solution
494	Target Sum	Python	given a sequence of ints, insert '+'s and '-'s to end up with target sum
496	Next Greater Element I	Python	classic stack
498	Diagonal Traverse	C++ Python	notice that if we add row and column of an element, we get an ID of a diagonal
503	Next Greater Element II	Python	given circular array find next greater number for every element, use stack
516	Longest Palindromic Subsequence	C++	classic dp
518	Coin Change 2	C++	classic dp, the number of combinations that make up the amount
530	Minimum Absolute Difference In BST	C++ Python	as title, in-order traversal
532	K Diff Pairs In An Array	Python	find all unique pairs for which diff equals k
539	Minimum Time Difference	Python	convert to minutes and sort
542	01 Matrix	Python	binary matrix, for each cell calculate distance from the neareast '0'. bfs.
543	Diameter Of Binary Tree	C++	logest path between any two nodes. Solve it by finding depths of subtrees
557	Reverse Words In A String III	C++ C Python	as title, loops
560	Subarray Sum Equals K	Python	total number of continuous subarrays whose sum equals to k, use hashing
575	Distribute Candies	Python	n candies given, can be of different types, take half and maximize number of different types
581	Shortest Unsorted Continuous Subarray	Python	find the shortest subarray to sort to end up with the whole array sorted, sort or use monotonic stack
583	Delete Operation For Two Strings	C++	given 2 strings w1 and w2, minimum number of steps to make them equal. dp
594	Longest Harmonious Subsequence	Python	a longest subsequence in which diff between min an max is exactly 1. hash map
617	Merge Two Binary Trees	C++	as title says
621	Task Scheduler	Python C++	python solution with heap and C++ more direct
630	Course Schedule III	C++	Each course has duration and deadline. Cannot do 2 courses at the same time. What's the max number that can be taken. Sort and then heap.
647	Palindromic Substrings	Python	number of palindroms in a string, dp
652	Find Duplicate Subtrees	Python	serialise e.g. using pre-order traversal
670	Maximum Swap	Python	in given int swap two digits at most once to get maximum value, greedy
680	Valid Palindrome II	C++	classic
684	Redundant Connection	C++ Python	build graph one edge at a time. Other solution brute force . grafy
698	Partition To K Equal Sum Subsets	C++	as title. dp with bitmasks
713	Subarray Product Less Than K	Python	find number of subarrays where the product of all the elements is less than given k, sliding window
714	Best Time To Buy And Sell Stock With Transaction Fee	Python
718	Maximum Length of Repeated Subarray	Python	two arrays given, longest common subarray, dp
735	Asteroid Collision	Python	classic stack problem with collisions
738	Monotone Increasing Digits	Python	Int has monotone increasing digits if each pair of adjacent digits x and y satisfy x <= y. Given int n, return largest int less or equal to n that has this characteristic.
739	Daily Temperatures	Python	for each day find number of days to wait for warmer temperature, use stack
743	Network Delay Time	C++ Python	Dijkstra's algorithm
752	Open The Lock	C++	graph problem, bfs. grafy
763	Partition Labels	C++	split array, got it on amzn interview
765	Couples Holding Hands	Python	Swap nums so that couples sit side by side. greedy, try also graph decomposition or union find. grafy
766	Toeplitz Matrix	C++	matrix is Toeplitz if every diagonal from top-left to bottom-right has the same elements
768	Max Chunks To Make Sorted II	C++ Python	array of ints. split array. then sort each chunk and concatenate to end up with sorted array. what's the max number of chunks. use map or max / min.
769	Max Chunks To Make Sorted	Python	array of n ints contains values 0 to n-1 and no duplicates. split array. then sort each chunk and concatenate to end up with sorted array. what's the max number of chunks.
779	K Th Symbol In Grammar	C++	start with 0, then in each round 0 turns into 01, 1 turns into 10, return Kth bit in Nth row, see pattern in tree and do recursion, try also one liner
785	Is Graph Bipartite	Python	can nodes be split into two groups and every edge connects these two groups, bfs or dfs. grafy
787	Cheapest Flights Within K Stops	Python	weighted graph given anf find the cheapest path from src to dst that has maximum K stops, dfs or bfs or other approaches. grafy
790	Domino And Tromino Tiling	C++	number of ways to tile a board 2xn using dominos and trominos. dp
829	Consecutive Numbers Sum	C++	number of ways an int can be written as a sum of consecutive ints. matma
837	New 21 Game	C++ Python	game with points, calculate probability
838	Push Dominoes	Python	dominoes falling, calculate final state.
847	Shortest Path Visiting All Nodes	C++	given path return shortest path visiting all nodes, start at any node. cause not many nodes use bitmask and bfs
854	K-Similar Strings	C++ Python	A and B are anagrams, find min number of swaps in A to make it equal to B, backtracking or BFS
862	Shortest Subarray With Sum At Least K	Python	Given int array nums and int k, return the length of the shortest non-empty subarray of nums with a sum of at least k. Monotone queue
870	Advantage Shuffle	Python	advantage of arr1 over arr2 is number of indexes where value in arr1 is greater than in arr2. return permutation of arr1 that maximizes its advantage. sort + pointers
871	Minimum Number Of Refueling Stops	C++	kind of jump game, heap or dp
873	Length Of Longest Fibonacci Subsequence	Python	brute force, try also dp
875	Koko Eating Bananas	C++	max speed that satisfies a specific condition, use binary search
877	Stone Game	C++	dp
881	Boats To Save People	C++	each person has weight, there's a max weight per boat and boat can only take 2 people, how many boats we need. sort and greedy
907	Sum Of Subarray Minimums	Python	sum mins for all subarrays, use stack
912	Sort An Array	C++ Python	implemet some classic sort algos, heap sort and quicksort
913	Cat And Mouse	C++	cat and mouse game on undirected graph. errichto dp top-down, try also other solutions. grafy
931	Minimum Falling Path Sum	Python	dp, similar to 1937
934	Shortest Bridge	Python	grid with 2 islands, find the shortest bridge, bfs to expand island 1 until we hit island 2
938	Minimum Cost For Tickets	C++ Python	array contains days on which i travel. i can buy 1, 7 or 30 days passes. find minimum i have to spend. dp
950	Reveal Cards In Increasing Order	C++ Python	arrange cards in a certain way
954	Array Of Doubled Pairs	C++ Python	re-arrange array so that each value has a pair twice as big
956	Tallest Billboard	C++ Python	given a set of rods construct supports for billboard, dp
957	Prison Cells After N Days	Python	cells become occupied or vacant, similar to bulbs, find cycle so we don't simulate it too many times
958	Check Completeness Of A Binary Tree	Python	as title. bfs.
969	Pancake Sorting	Python	should be self descriptive
973	K Closest Points To Origin	Python	as title. sorting.
979	Distribute Coins In Binary Tree	Python	re-distribute coins in tree so that every node has exactly one. dfs
988	Smallest String Starting From Leaf	C++	dfs
990	Satisfiability Of Equality Equations	C++	check if a set of equations with '!=' and '==' can be satisfied. classic dfs and union find
991	Broken Calculator	Python	go from int X to int Y, with min number of steps, can only multiply by 2 and subtract 1. go backwards from Y to X
992	Subarrays With K Different Integers	Python	int array nums and int k given, return the number of good subarrays. in good array number of different ints is exactly k. sliding window
994	Rotting Oranges	C++	matrix problem, to solve do simulation
996	Number Of Squareful Arrays	C++	find array permutations that would result in squarefl array, brute force or kind of Hamiltonian problem
1004	Max Consecutive Ones III	C++	binary array and we can flip at most k '0's. What's the longest sequence of '1' we can get. Special case also solved in cpp file - what if only one '0' can be flipped. Classic sliding window.
1007	Minimum Domino Rotations For Equal Row	C++	row of dominos give. If we can rotate some of them to get same value in a row, what's the minimum number of rotations.
1008	Construct Binary Search Tree From Preorder Traversal	C++ Python	as title. recursion.
1024	Video Stitching	Python	cut and stitch clips so they cover the whole interval, find min number of cuts to do it, sort and greedy
1031	Maximum Sum Of Two Non Overlapping Subarrays	C++	title says it all also Alice and Bob picking Apples
1048	Longest String Chain	C++	list of strings. given s1 you arrive at s2 by adding a char. find longest chain. dp bfs
1081	Smallest Subsequence Of Distinct Characters	Python	hashing and intuition
1092	Shortest Common Supersequence	C++ Python	Given two strings, return the shortest string that has both as subsequences. LCS. DFS + memiozation gets memory limit exceeded
1109	Corporate Flight Bookings	C++	sweep line algo
1110	Delete Nodes And Return Forest	C++	dfs
1124	Longest Well Performing Interval	Python	binary array, find longest subarray with more 1s than 0s, hashing to solve in linear time
1143	Longest Common Subsequence	Python	two strings and find LCS, dp
1178	Number Of Valid Words For Each Puzzle	C++	string play. bitmasks.
1186	Maximum Subarray Sum With One Deletion	Python	Kadane algo twice - one forward and one backward
1192	Critical Connections In A Network	Python	removing what edges would result in disconnected graph. Tarjan's strongly connected components algorithm. grafy
1209	Remove All Adjacent Duplicates In String II	C++	given string s and int k, do all k duplicate removals, stack
1219	Path With Maximum Gold	C++	in grid find path with maximum gold. dfs.
1221	Split A String In Balanced Strings	C++	split binary string in balanced substrings
1222	Queens That Can Attack The King	Python	given positions of king and queens, find queens that are attacking the king. solve by simulation.
1239	Maximum Length Of A Concatenated String With Unique Characters	C++	glue strings together, needs to have unique chars, dfs + bitmasks, string play
1244	Design A Leaderboard	C++	locked on lc, top K stocks on blmbrg interview, keep track of stocks traded and impement a function to print K most traded, hash map (to map stock to volume) and multimap (to map volume to stock)
1247	Minimum Swaps To Make Strings Equal	Python	two binary strings s1 and s2, can only swap chars between s1 and s2, minimum swaps to make them equal
1249	Minimum Remove To Make Valid Parentheses	C++	stack solution
1268	Search Suggestions System	C++	as title. good practise
1305	All Elements In Two Binary Search Trees	C++	in-order traversal and merge
1306	Jump Game III	Python	can jump by arr[i] left or right, can we reach any index with value 0. recursion.
1325	Delete Leaves With A Given Value	C++	dfs
1338	Reduce Array Size To The Half	C++	Choose a set of ints from array and remove all their occurrences. Return the minimum size of the set so that at least half of the integers of the array are removed. Sort + greedy.
1340	Jump Game V	Python	jump to any index closer than d if no higher blocks between. max number of blocks to visit. sort + dp
1345	Jump Game IV	Python	can jump back or forward by 1 or to any index with the same value as the curren one. bfs
1367	Linked List In Binary Tree	C++	bfs + dfs
1368	Cinema Seat Allocation	Python	as title. hash map and can use bitmasks
1381	Design A Stack With Increment Operation	C++	stack with an operation that increments last k elements. lazy evaluation
1382	Balance A Binary Search Tree	C++	given a root of BST, return a balanced BST, easy solution - in order traversal to collect numbers then construct balanced BST, try also DSW algorithm
1395	Count Number Of Teams	Python	basically in ints array find triplets that increase, in O(N^2) easy, try also balanced tree and bs
1405	Longest Happy String	C++	string composed only of 'a', 'b', 'c'. Cannot have triplets (e.g. 'bbb'). Can have at most a occurences of 'a', b of 'b', c of 'c'.Construct longest possible. Similar to 621 (Task Scheduler)
1442	Count Triplets That Can Form Two Arrays Of Equal XOR	C++	basically comes down to find all subarrays for which XOR is 0.
1443	Minimum Time To Collect All Apples In A Tree	Python	a tree that has apples on some nodes, min number of moves to collect all of them. dfs.
1444	Number Of Ways Of Cutting A Pizza	C++	cut pizza into k slices so that each has at least one apple. dp
1462	Course Schedule IV	Python	queries about dependencies in graph. dfs or topological sort. grafy
1488	Avoid Flood In The City	C++	info in solution file
1509	Minimum Difference Between Largest And Smallest Value In Three Moves	C++	in array in 3 moves minimize diff between max and min value
1514	Path with Maximum Probability	C++	Dijkstra's algorithm
1528	Shuffle String	C++	shuffle string according to the mapping given
1530	Number Of Good Leaf Nodes Pairs	C++	count leaves pairs with shortest path smaller than k. bfs. try also dfs
1559	Detect Cycles In 2D Grid	C++ Python	as title. graph problem. dfs or bfs. grafy
1567	Maximum Length Of Subarray With Positive Product	C++	as title. dp
1579	Remove Max Number Of Edges To Keep Graph Fully Traversable	Python	some edges usable by A, some by B, some by both. max number of edges we can remove so A and B can still traverse the graph. greedy with union find. grafy
1584	Min Cost To Connect All Points	Python	minimum spanning tree
1642	Furthest Building You Can Reach	C++	jump between buildings using ladder and bricks. heap.
1643	Kth Smallest Instructions	C++ Python	combinations with duplicates
1685	Sum Of Absolute Differences In A Sorted Array	Python	for each element in array find sum of abs differences, use formula to do it in O(N)
1694	Reformat Phone Number	Python	at title. regex or loops
1705	Maximum Number Of Eaten Apples	C++	each day apples grow and rot, how many can we eat, heap
1711	Count Good Meals	C++	in array find all pairs that sum up to any power of 2. hash map
1726	Tuple With Same Product	C++	array of distinct positive ints, find all tuples a,b,c,d such that ab=cd
1739	Building Boxes	Python	stack boxes according to rules. find minimum number of boxes on the floor. matma
1751	Maximum Number Of Events That Can Be Attended II	C++ Python	each event has start, end and value. pick at most k events to maximize sum of values. dp and bs. good practise.
1775	Equal Sum Arrays With Minimum Number Of Operations	C++ Python	modify values in arrays to make sums equal. greedy approach.
1781	Sum Of Beauty Of All Substrings	C++	beauty of string is diff in freq between most and last frequent chars, sum beauties of all substrings, hashing
1793	Maximum Score Of A Good Subarray	C++ Python	a tricky to prove greedy solution, also solution for LC 84 Largest Rectangle in Histogram works here
1797	Design Authentication Manager	C++	use hashmap and set
1814	Count Nice Pairs In An Array	C++ Python	transform formula and then use hashing
1871	Jump Game VII	C++	jump on stones if jump length between min and max. bfs
1884	Egg Drop With 2 Eggs And N Floors	C++ Python	as title
1937	Maximum Number Of Points With Cost	C++	dp
1942	The Number Of The Smallest Unoccupied Chair	C++	numbered chairs taken/freed by arriving/leaving guests. What chair will be taken by a concrete guest. sort times. use hash map and heap.
1986	Minimum Number Of Work Sessions To Finish The Tasks	C++	distribute tasks into min number of sessions. dfs + memo. try also bitmap
2002	Maximum Product Of The Length Of Two Palindromic Subsequences	C++	as title. dfs, try also other methods
2054	Two Best Non Overlapping Events	Python	each event has begin, end and value. sort + bs
2080	Range Frequency Queries	C++	query[l,r,v] to see how many files value v appears in the array between indexes l and r. binary search.
2096	Step By Step Directions From A Binary Tree Node To Another	Python	use lowest common ancestor solution
2104	Sum Of Subarray Ranges	Python	almost same as Sum Of Subarray Minimums, one pass for min and one for max
2134	Minimum Swaps To Group All 1s Together II	Python	Given a binary circular array nums, return the minimum number of swaps required to group all 1s present in the array together at any location. Sliding window.
2135	Count Words Obtained After Adding A Letter	C++	add char and reshuffle to see if can arrive at other string, bitmask + hash map, try also sort and trie, string play
2145	Count The Hidden Sequences	Python	given array of diffs between consecutive elements in a hidden array. Also given max and min element that can be in the hidden array. Find number of possible hidden arrays. matma
2163	Minimum Difference In Sums After Removal Of Elements	C++	array has 3 * n ints, remove n elements to minimize left - right, left is sum of first n elements after removal, right is sum of last n. heap
2178	Maximum Split Of Positive Even Integers	Python	Split a given int into a sum of a maximum number of unique positive even integers. greedy.
2182	Construct String With Repeat Limit	C++	given string s, reuse its chars and construct a new one lexicographically biggest. Limit on number of repetitions.
2195	Append K Integers With Minimal Sum	C++	given int array nums and an int k. Append k unique positive ints that do not appear in nums so that the resulting total sum is minimum. sort and Gauss formula.
2203	Minimum Weighted Subgraph With The Required Paths	C++	directed graph, nodes src1 src2 dest given, find minimum weight of a subgraph in which it's possible to reach dest from both src1 and src2, Dijkstra. grafy
2272	Substring With Largest Variance	C++	as title. for each pair of chars run modified Kanane algo for finding subarray with largest sum
2275	Largest Combination With Bitwise AND Greater Than Zero	C++	Given int array arr return size of largest combination of vals with a bitwise AND greater than 0. Iterate over 32 bits and nested loop over array
2312	Selling Pieces Of Wood	Python	divide a piece of wood into pieces (only certain sizes possible) to be sold. What's the optimal division. dp
2316	Count Unreachable Pairs Of Nodes In An Undirected Graph	Python	as title. dfs or union find. grafy
2349	Design A Number Container System	C++	design data structure that maps index to number, function find should return the smallest index for given number. two hash maps
2360	Longest Cycle In A Graph	C++	directed graph given, each node has at most one outgoing edge. find longest cycle. dfs. grafy
2364	Count Number Of Bad Pairs	Python	transform formula and then use hashing
2366	Minimum Replacements To Sort The Array	Python	matma
2375	Construct Smallest Number From DI String	Python	string with chars D (decrease) and I (increase) given. using digits construct smallest number. kind of greedy or backtracking
2376	Count Special Integers	Python	int is special if all its digits are distinct. count all special ints smaller than given n. combinatorics. matma
2381	Shifting Letters II	Python	line sweep algo
2434	Using A Robot To Print The Lexicographically Smallest String	Python	strings manipulations, greedy
2435	Paths In Matrix Whose Sum Is Divisible By K	C++	as title. dp
2439	Minimize Maximum Of Array	C++ Python	matma
2448	Minimum Cost To Make Array Equal	Python	as title. prefix sum.
2467	Most Profitable Path In A Tree	Python	bfs dfs good practise
2470	Number Of Subarrays With LCM Equal To K	C++	least common multiple. use library function to solve. for greatest common divisor similar solution
2508	Add Edges To Make Degrees Of All Nodes Even	Python	can add max two edges so that every node in the graph has even degree. grafy
2513	Minimize The Maximum Of Two Arrays	C++	fill arrays with values omitting ones that are divisible by certain ints. lcm, bs, matma
2542	Maximum Subsequence Score	C++	two arrays of same size, pick subsequence of indexes of length k to maximize sum from nums1 multiplied by min from nums2. sort and heap
2543	Check If Point Is Reachable	Python	starting at 2d point, some transformations allowed. can we reach destination. greedy or maths. matma.
2565	Subsequence With The Minimum Score	C++	remove chars from t so that it becomes a subsequence of s. dp
2608	Shortest Cycle In A Graph	Python	as title. dfs. grafy.
2659	Make Array Empty	Python	rotate to move smallest el to front then remove it. keep doing that. number of operations. sort.
2685	Count The Number Of Complete Components	C++	as title. count edges and nodes. grafy
2712	Minimum Cost To Make All Characters Equal	Python	binary string. flip values. dp. good practise.
2799	Count Complete Subarrays In An Array	C++	count subarrays that have same number of distinct elements as whole array. sliding window
2856	Minimum Array Length After Pair Removals	C++	sorted array, keep cancelling elements, how many left. tricky intuition. matma
2919	Minimum Increment Operations To Make Array Beautiful	Python	given array and k. do increments till all subarrays of length 3 have at least one element k. dp. try also other methods
2957	Remove Adjacent Almost Equal Characters	C++	in a move we can pick index and modify char in string. minimum moves to arrive at string in which there's no adjacent chars that are same of diff by 1. greedy
no number	Candy Crush 1D	C++	candy crush in 1D, blmbrg interview

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