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Software Engineer Interview

Author: [email protected]

Table of Contents

Interview Preparation

Leadership and Management

Languages and Data Structures

Java

Java is a general-purpose programming language that is class-based, object-oriented, and designed to have as few implementation dependencies as possible. It is intended to let application developers write once, run anywhere, meaning that compiled Java code can run on all platforms that support Java without the need for recompilation.

Java Overview and Features

Data Structures in Java

Python

Python is an interpreted, high-level, general-purpose programming language. Python's design philosophy emphasizes code readability with its notable use of significant whitespace (indentation). Python is dynamically typed and garbage-collected.

Python Overview and Features

Data Structures in Python

  • Array and Sequence
    • Range
    • String
    • List
    • Tuple
      • NamedTuple
  • Linked List
    • Singly Linked List
    • Doubly Linked List
  • Collections
    • Deque
  • Dictionary
    • OrderedDict
    • DefaultDict
    • UserDict
  • Set
  • Bytearray
  • Tree
  • Graph

Go

Go is a statically typed, compiled programming language designed at Google. Go is syntactically similar to C, but with memory safety, garbage collection, structural typing, and CSP-style concurrency.

Go Overview and Features

Data Structures in Go

  • Basic Data Structures
    • Array
    • Slice
    • Map
    • Struct
  • Linked List
  • Queue
  • Stack
  • Set
  • Tree
  • Graph

Algorithms

Algorithm is one of core parts in computer science. This section covers the algorithms in tech interviews.

An algorithm must possess the following five properties:

  • input: an algorithm has zero or more inputs, taken from a specified set of objects.
  • output: an algorithm has one or more outputs, which have a specified relation to the inputs.
  • finiteness: the algorithm must always terminate after a finite number of steps.
  • definiteness: Each step must be precisely defined; the actions to be carried out must be rigorously and unambiguously specified for each case.
  • effectiveness: all operations to be performed must be sufficiently basic that they can be done exactly and in finite length.

As the restriction of whiteboard coding and the properties of algorithm, most of interview questions can be resolved in ~50 lines of code.

Computational Complexity

The computational complexity of an algorithm is the amount of resources required to run it. Particular focus is given to time and space requirements.

Basic Algorithms

Sort Algorithms

Sorting algorithm is an algorithm that puts elements of a list in a certain order. The most frequently used orders are numerical order and lexicographical order. Efficient sorting is important for optimizing the efficiency of other algorithms (such as search and merge algorithms) that require input data to be in sorted lists. Sorting is also often useful for canonicalizing data and for producing human-readable output.

O(n^2) Solutions

O(nlogn) Solutions

O(n) Solutions

Search Algorithms

Graph Search

Linear List Search

Search Tree

  • Binary Search Tree
  • B-tree
  • (a,b)-tree

Other Algorithms

It is very rare to see bit or math questions in real interviews. So we don't need to spend lots of time here.

More Readings

System Design

  • System Design Basics
    • Distributed System
    • Cluster
    • Load Balancing
    • Message Queue
    • Cache
      • CDN
    • Database
      • SQL
      • NoSQL
    • Networking
      • Networking Basic
      • HTTP
      • RESTful API
      • WebSocket
    • Security
  • Popular System Design Questions
    • Designing a URL shortening service
    • Designing Instagram
    • Designing Facebook Messenger
    • Designing Facebook Newsfeed

The purpose of a system design interview is to assess a candidate's ability to design and understand complex systems. It's a crucial part of the hiring process for roles that involve system architecture and engineering.

The general approach I'd like to suggest is,

  • Requirements Gathering
    • Gather functional & non-functional requirements
      • Functional requirements
        • Users can do A, B, C, D
      • Non-functional requirements
        • Availability
        • Scalability
        • Reliability
        • Performance
          • Round-Trip Time (RTT) or Latency
          • Throughput or Bandwidth
    • Clarify restrictions and limitations
    • Estimate system resources
  • Decision-making Process
    • High level design
      • System architecture
      • Service API
      • Data schema
    • Component walkthrough
    • Optimization
  • Balancing Trade-offs

Coding Preparation

How to use LeetCode

LeetCode Current Status

LintCode Current Status

Notes

  • I use LintCode as the supplement of LeetCode for the locked questions.
  • I usually skip the hard math questions, since it is almost impossible to see them in a real interview.

Easy Questions

# Name Solution Algorithm Note
1 Two Sum Java Python Go HashMap
7 Reverse Integer Java Number
9 Palindrome Number Java Number
13 Roman to Integer Java Map
14 Longest Common Prefix Java Loop More solutions
20 Valid Parentheses Java Python Stack
21 Merge Two Sorted Lists Java Loop
26 Remove Duplicates from Sorted Array Java Two-Pointer
27 Remove Element Java Single Pointer
28 Implement strStr() Java String
35 Search Insert Position Java String
38 Count and Say Java Number
53 Maximum Subarray Java DP
58 Length of Last Word Java String
66 Plus One Java Loop
67 Add Binary Java Loop
69 Sqrt(x) Java Math Apply Newton's Method
70 Climbing Stairs Java 1D DP
83 Remove Duplicates from Sorted List Java Two-Pointer
88 Merge Sorted Array Java Two-Pointer
100 Same Tree Java Recursion
101 Symmetric Tree Java Recursion
104 Maximum Depth of Binary Tree Java DFS
107 Binary Tree Level Order Traversal II Java DFS + BFS
108 Convert Sorted Array to Binary Search Tree Java Recursion
110 Balanced Binary Tree Java DFS
111 Minimum Depth of Binary Tree Java DFS
112 Path Sum Java DFS
118 Pascal's Triangle Java Array
119 Pascal's Triangle II Java 1D DP
121 Best Time to Buy and Sell Stock Java DP
122 Best Time to Buy and Sell Stock II Java Greedy
125 Valid Palindrome Java Two-Pointer
136 Single Number Java Bit
141 Linked List Cycle Java LinkedList
155 Min Stack Java Python Stack
157 Read N Characters Given Read4 Java Stream
160 Intersection of Two Linked Lists Java Python LinkedList
167 Two Sum II - Input array is sorted Java Two-Pointer
168 Excel Sheet Column Title Java Math
169 Majority Element Java Array Moore's voting algorithm
170 Two Sum III - Data structure design Java HashMap
171 Excel Sheet Column Number Java Math
172 Factorial Trailing Zeroes Java Math
189 Rotate Array Java Array
190 Reverse Bits Java Bit
191 Number of 1 Bits Java Bit
198 House Robber Java 1D DP
202 Happy Number Java Set
203 Remove Linked List Elements Java LinkedList
204 Count Primes Java Math Sieve of Eratosthenes
205 Isomorphic Strings Java Map
206 Reverse Linked List Java LinkedList
217 Contains Duplicate Java Set
219 Contains Duplicate II Java Two-Pointer
225 Implement Stack using Queues Java Queue
226 Invert Binary Tree Java DFS
228 Summary Ranges Java Two-Pointer
231 Power of Two Java Bit Manipulation
252 Meeting room Java Array LintCode
232 Implement Queue using Stacks Java Stack
234 Palindrome Linked List Java Two-Pointer Reversing a list is not considered "O(1) space"
235 Lowest Common Ancestor of a Binary Search Tree Java DFS
237 Delete Node in a Linked List Java LinkedList This is a stupid question
242 Valid Anagram Java Counting Sort
243 Shortest Word Distance Java Greedy LintCode 924
246 Strobogrammatic Number Java Two-Pointer LintCode 644
252 Meeting Rooms Java Sort LintCode 920
256 Paint House Java 1D DP LintCode 515 as medium
257 Binary Tree Paths Java DFS
258 Add Digits Java Number
263 Ugly Number Java Math
266 Palindrome Permutation Java Counting sort LintCode 916
268 Missing Number Java Counting Bit manipulation solution using XOR is here
270 Closest Binary Search Tree Value Java DFS LintCode 900
276 Paint Fence Java 1D DP LintCode 514
278 First Bad Version Java Binary Search
283 Move Zeroes Java Two-Pointer
290 Word Pattern Java HashMap
292 Nim Game Java Minimax
293 Flip Game Java Loop LintCode 914
299 Bulls and Cows Java Counting
303 Range Sum Query - Immutable Java Segment Tree
326 Power of Three Java Math
339 Nested List Weight Sum Java Recursion LintCode 551
344 Reverse String Java Two Pointer
346 Moving Average from Data Stream Java Sliding Window LintCode 642
367 Valid Perfect Square Java Math
374 Guess Number Higher or Lower Java Binary Search
383 Ransom Note Java Letter Count
401 Binary Watch Java bit
408 Valid Word Abbreviation Java String LintCode 637
409 Longest Palindrome Java String
422 Valid Word Square Java String LintCode 888
437 Path Sum III Java DFS Deserve as medium
443 String Compression Java Two-Pointer
459 Repeated Substring Pattern Java String
485 Max Consecutive Ones Java 1D DP
530 Minimum Absolute Difference in BST Java In-order Traversal
541 Reverse String II Java Two Pointer
543 Diameter of Binary Tree Java DFS
551 Student Attendance Record I Java Array
557 Reverse Words in a String III Java Two Pointer
561 Array Partition I Java Math
572 Subtree of Another Tree Java Recursion Converting to string is a brilliant idea
575 Distribute Candies Java Greedy
594 Longest Harmonious Subsequence Java HashMap
628 Maximum Product of Three Numbers Java Greedy?
680 Valid Palindrome II Java String
700 Search in a Binary Search Tree Java BinarySearch
703 Kth Largest Element in a Stream Java MinQueue
704 Binary Search Java BinarySearch
709 To Lower Case Java String
720 Longest Word in Dictionary Java HashSet
724 Find Pivot Index Java Prefix/Suffix Sum
728 Self Dividing Numbers Java Math
733 Flood Fill Java DFS
748 Shortest Completing Word Java String
746 Min Cost Climbing Stairs Java 1D DP
766 Toeplitz Matrix Java Matrix
771 Jewels and Stones Java Set
783 Minimum Distance Between BST Nodes Java DFS
788 Rotated Digits Java DP There is O(lgn) solution, but very tricky!
796 Rotate String Java String The rolling hash solution is great!
821 Shortest Distance to a Character Java MinArray
852 Peak Index in a Mountain Array Java BinarySearch
844 Backspace String Compare Java Stack Two pointers starting from the end is better in term of space performance
849 Maximize Distance to Closest Person Java DP
859 Buddy Strings Java StringLoop/LetterCount
860 Lemonade Change Java Greedy
867 Transpose Matrix Java Loop
872 Leaf-Similar Trees Java DFS
876 Middle of the Linked List Java LinkedList
884 Uncommon Words from Two Sentences Java String
905 Sort Array By Parity Java Array
908 Smallest Range I Java Math
917 Reverse Only Letters Java Two-Pointer
922 Sort Array By Parity II Java Read/Write Head
994 Rotting Oranges Java BFS
1022 Sum of Root To Leaf Binary Numbers Java DFS
1025 Divisor Game Java 1D DP Solution with constant time
1047 Remove All Adjacent Duplicates In String Java Stack
1281 Subtract the Product and Sum of Digits of an Integer Java Number
1337 The K Weakest Rows in a Matrix Java MaxQueue

Medium Questions

# Name Solution Algorithm Note
2 Add Two Numbers Java Python Linked List
3 Longest Substring Without Repeating Characters Java Two-Pointer
5 Longest Palindromic Substring Java 2D DP Manacher's Algorithm is the optimal solution
6 ZigZag Conversion Java String
8 String to Integer (atoi) Java String
11 Container With Most Water Java Two-Pointer/Greedy
12 Integer to Roman Java Number
15 Three Sum Java Python Two-Pointer
16 3Sum Closest Java Python Two-Pointer
17 Letter Combinations of a Phone Number Java Backtracking (DFS)
18 4Sum Java Two-Pointer
19 Remove Nth Node From End of List Java Two-Pointer
22 Generate Parentheses Java Python Backtracking (DFS)
24 Swap Nodes in Pairs Java Recursion
29 Divide Two Integers Java Bit
31 Next Permutation Java Math
33 Search in Rotated Sorted Array Java Binary Search
34 Find First and Last Position of Element in Sorted Array Java Binary Search
36 Valid Sudoku Java Matrix
39 Combination Sum Java Backtracking (DFS)
40 Combination Sum II Java Backtracking (DFS)
43 Multiply Strings Java Loop
46 Permutations Java Backtracking (BFS & DFS)
47 Permutations II Java Backtracking (BFS & DFS)
48 Rotate Image Java Matrix
49 Group Anagrams Java HashMap/String Signature
50 Pow(x, n) Java Math
54 Spiral Matrix Java Matrix
55 Jump Game Java Greedy
56 Merge Intervals Java Sort
59 Spiral Matrix II Java Matrix
60 Permutation Sequence Java Math
61 Rotate List Java LinkedList
62 Unique Paths Java 2D DP
63 Unique Paths II Java 2D DP
64 Minimum Path Sum Java 2D DP
71 Simplify Path Java Stack
73 Set Matrix Zeros Java Matrix
74 Search a 2D Matrix Java Binary Search
75 Sort Colors Java Two-Pointer
77 Combinations Java Backtracking (DFS)
78 Subsets Java Backtracking (BFS & DFS)
79 Word Search Java Backtracking (DFS)
80 Remove Duplicates from Sorted Array II Java Two-Pointer
81 Search in Rotated Sorted Array II Java Binary Search
82 Remove Duplicates from Sorted List II Java LinkedList
86 Partition List Java LinkedList
89 Gray Code Java Bit
90 Subsets II Java Backtracking (BFS & DFS)
91 Decode Ways Java 1D DP
92 Reverse Linked List II Java LinkedList
93 Restore IP Addresses Java Backtracking & Greedy
94 Binary Tree Inorder Traversal Java Tree Traversal
95 Unique Binary Search Trees II Java DFS
96 Unique Binary Search Trees Java 1D DP Optimized from 2D to 1D
98 Validate Binary Search Tree Java DFS
102 Binary Tree Level Order Traversal Java Python DFS & BFS
103 Binary Tree Zigzag Level Order Traversal Java DFS & BFS
105 Construct Binary Tree from Preorder and Inorder Traversal Java Recursion
106 Construct Binary Tree from Inorder and Postorder Traversal Java Recursion
109 Convert Sorted List to Binary Search Tree Java D&C
113 Path Sum II Java Backtracking (DFS)
114 Flatten Binary Tree to Linked List Java BFS & DFS
116 Populating Next Right Pointers in Each Node Java Loop
117 Populating Next Right Pointers in Each Node II Java Loop
120 Triangle Java 1D DP
127 Word Ladder Java Backtracking (BFS & DFS) LeetCode needs some optimization to pass TLE, which I think is an overkill
129 Sum Root to Leaf Numbers Java DFS
130 Surrounded Regions Java BFS & DFS Union Find solution
131 Palindrome Partitioning Java Backtracking (DFS) + DP + Recursion
133 Clone Graph Java DFS + BFS
134 Gas Station Java Greedy
137 Single Number II Java Bit + Set Great explanation of this type of questions is here
138 Copy List with Random Pointer Java HashMap Space complexity can be optimized to O(1) as here
139 Word Break Java 1D DP
142 Linked List Cycle II Java LinkedList
143 Reorder List Java LinkedList
144 Binary Tree Preorder Traversal Java Stack
146 LRU Cache Java HashMap & DoublyLinkedList Deserve as hard
147 Insertion Sort List Java LinkedList
148 Sort List Java LinkedList
150 Evaluate Reverse Polish Notation Java Stack
151 Reverse Words in a String Java String Should be an easy one
152 Maximum Product Subarray Java 1D DP
153 Find Minimum in Rotated Sorted Array Java Binary Search
156 Binary Tree Upside Down Java Stack LintCode 649
159 Longest Substring with At Most Two Distinct Characters Java Two-Pointer LintCode 928
161 One Edit Distance Java String LintCode 640
162 Find Peak Element Java BinarySearch
163 Missing Ranges Java Loop LintCode 641
165 Compare Version Numbers Java String
166 Fraction to Recurring Decimal Java HashMap Should be as hard
173 Binary Search Tree Iterator Java BFS+Stack
179 Largest Number Java Sort
186 Reverse Words in a String II Java Two-Pointer LintCode 927
187 Repeated DNA Sequences Java HashMap
199 Binary Tree Right Side View Java DFS & BFS
200 Number of Islands Java DFS & BFS
201 Bitwise AND of Numbers Range Java Bit
207 Course Schedule Java Topological Sort
208 Implement Trie (Prefix Tree) Java Trie
209 Minimum Size Subarray Sum Java Sliding Window
210 Course Schedule II Java Topological Sort
211 Add and Search Word - Data structure design Java Trie+Backtracking
213 House Robber II Java 1D DP
215 Kth Largest Element in an Array Java Heap Sort A better solution uses Selection algorithm with shuffling
216 Combination Sum III Java Backtracking (DFS)
220 Contains Duplicate III Java TreeMap TLE on LeetCode OJ (it's a boring question)
221 Maximal Square Java DP
222 Count Complete Tree Nodes Java DFS
223 Rectangle Area Java Math
227 Basic Calculator II Java Deque A better solution uses a single stack
229 Majority Element II Java Boyer-Moore Majority Voting Algorithm
230 Kth Smallest Element in a BST Java DFS
236 Lowest Common Ancestor of a Binary Tree Java DFS
238 Product of Array Except Self Java 1D DP This solution uses O(1) space
240 Search a 2D Matrix II Java Divide and Conquer
241 Different Ways to Add Parentheses Java Recursion
247 Strobogrammatic Number II Java Recursion LintCode 776
250 Count Univalue Subtrees Java DFS LintCode 921
251 Flatten 2D Vector Java Two-Pointer LintCode 601
253 Meeting Rooms II Java Sweep Line Algorithm LintCode 919
254 Factor Combinations Java Backtracking (DFS) LintCode 1308
255 Verify Preorder Sequence in Binary Search Tree Java Divide and Conquer LintCode 1307
259 3Sum Smaller Java Two-Pointer LintCode 918
260 Single Number III Java Bit It's a hard question to achieve Space O(1)
261 Graph Valid Tree Java UnionFind LintCode 178
264 Ugly Number II Java 1D DP
267 Palindrome Permutation II Java Backtracking (DFS) LintCode 917
271 Encode and Decode Strings Java String LintCode 659
274 H-Index Java Sort & Map
275 H-Index II Java BinarySearch
277 Find the Celebrity Java Two-Pointer & Stack & Graph LintCode 645
279 Perfect Squares Java 1D DP
280 Wiggle Sort Java Greedy LintCode 508
281 Zigzag Iterator Java List LintCode 540
284 Peeking Iterator Java Design
285 Inorder Successor in BST Java DFS LintCode 448
286 Walls and Gates Java BFS LintCode 663
287 Find the Duplicate Number Java Two-Pointer
288 Unique Word Abbreviation Java HashMap LintCode 648
289 Game of Life Java Bit
294 Flip Game II Java Backtracking (DFS) LintCode 913
298 Binary Tree Longest Consecutive Sequence Java DFS LintCode 595
300 Longest Increasing Subsequence Java 1D DP Binary search solution is more optimal
304 Range Sum Query 2D - Immutable Java Matrix
306 Additive Number Java Backtracking (DFS)
307 Range Sum Query - Mutable Java Segment Tree
309 Best Time to Buy and Sell Stock with Cooldown Java 1D DP
310 Minimum Height Trees Java BFS
311 Sparse Matrix Multiplication Java List LintCode 654
314 Binary Tree Vertical Order Traversal Java DFS + HashMap LintCode 651 (LintCode OJ is incorrect)
318 Maximum Product of Word Lengths Java Bit-Manipulation
319 Bulb Switcher Java Math
320 Generalized Abbreviation Java Backtracking (DFS) LintCode 779
322 Coin Change Java 1D DP
325 Maximum Size Subarray Sum Equals k Java HashMap LintCode 911
328 Odd Even Linked List Java LinkedList
331 Verify Preorder Serialization of a Binary Tree Java DFS Non-cursive solution based on graph theory
332 Reconstruct Itinerary Java Greedy
334 Increasing Triplet Subsequence Java Loop
337 House Robber III Java Backtracking (DFS)
338 Counting Bits Java Bit
341 Flatten Nested List Iterator Java Recursion
343 Integer Break Java Math
347 Top K Frequent Elements Java HashMap + Heap
357 Count Numbers with Unique Digits Java Math
361 Bomb Enemy Java DP LintCode 553
366 Find Leaves of Binary Tree Java DFS LintCode 650
369 Plus One Linked List Java Recursion LintCode 904
370 Range Addition Java Array LintCode 903
373 Find K Pairs with Smallest Sums Java Heap
376 Wiggle Subsequence Java 1D DP
377 Combination Sum IV Java 1D DP
378 Kth Smallest Element in a Sorted Matrix Java Min Heap
380 Insert Delete GetRandom O(1) Java HashMap
382 Linked List Random Node Java LinkedList It's essentially a math question (Reservoir Sampling).
384 Shuffle an Array Java Math Fisher–Yates shuffle
385 Mini Parser Java Recursion
386 Lexicographical Numbers Java DFS
388 Longest Absolute File Path Java Stack
394 Decode String Java Stack & DFS Deserve as hard
397 Integer Replacement Java Bit
402 Remove K Digits Java Greedy
406 Queue Reconstruction by Height Java Greedy
413 Arithmetic Slices Java 1D DP
416 Partition Equal Subset Sum Java DP Knapsack Model
417 Pacific Atlantic Water Flow Java BFS
418 Sentence Screen Fitting Java Looping LintCode 889
419 Battleships in a Board Java Greedy Should be as easy
423 Reconstruct Original Digits from English Java Math
424 Longest Repeating Character Replacement Java Two-Pointer
430 Flatten a Multilevel Doubly Linked List Java Recursion
433 Minimum Genetic Mutation Java Backtracking (DFS)
435 Non-overlapping Intervals Java Sort + 1D DP Greedy solution can optimize to O(nlogn)
436 Find Right Interval Java TreeMap & Binary Search
438 Find All Anagrams in a String Java Sliding Window
439 Ternary Expression Parser Java Backtracking (DFS) LintCode 887
442 Find All Duplicates in an Array Java Array
445 Add Two Numbers II Java Stack
451 Sort Characters By Frequency Java Counting Sort
453 Minimum Moves to Equal Array Elements Java Math
454 4Sum II Java HashMap
456 132 Pattern Java Array OJ
452 Minimum Number of Arrows to Burst Balloons Java Greedy
474 Ones and Zeroes Java 3D DP Knapsack Model
477 Total Hamming Distance Java Bit
486 Predict the Winner Java 2D DP
491 Increasing Subsequences Java Backtracking (DFS)
494 Target Sum Java Backtracking (DFS) 1D DP solution
495 Teemo Attacking Java Greedy
498 Diagonal Traverse Java Matrix Looping
503 Next Greater Element II Java Stack
513 Find Bottom Left Tree Value Java DFS
515 Find Largest Value in Each Tree Row Java DFS
516 Longest Palindromic Subsequence Java 2D DP
523 Continuous Subarray Sum Java Math
539 Minimum Time Difference Java String
542 01 Matrix Java Stack
560 Subarray Sum Equals K Java HashMap
567 Permutation in String Java Sliding Window
611 Valid Triangle Number Java Sort
662 Maximum Width of Binary Tree Java DFS
670 Maximum Swap Java Array
678 Valid Parenthesis String Java Greedy + Backtracking It can be solved by DP, greedy and backtracking!
725 Split Linked List in Parts Java LinkedList
729 My Calendar I Java Interval
739 Daily Temperatures Java Stack
791 Custom Sort String Java Bucket Sort
856 Score of Parentheses Java Stack
870 Advantage Shuffle Java Greedy + BinarySearch
881 Boats to Save People Java Greedy + Two-Pointer
916 Word Subsets Java String Signature
921 Minimum Add to Make Parentheses Valid Java Greedy
958 Check Completeness of a Binary Tree Java BFS
986 Interval List Intersections Java Two-Pointer
1048 Longest String Chain Java 1D DP
1091 Shortest Path in Binary Matrix Java BFS
1110 Delete Nodes And Return Forest Java DFS
1202 Smallest String With Swaps Java UnionFind + PriorityQueue Deserve as hard
1249 Minimum Remove to Make Valid Parentheses Java Greedy
1302 Deepest Leaves Sum Java DFS
1306 Jump Game III Java Backtracking (DFS)
1315 Sum of Nodes with Even-Valued Grandparent Java DFS
1339 Maximum Product of Splitted Binary Tree Java DFS
1423 Maximum Points You Can Obtain from Cards Java DP & Sliding Window
1642 Furthest Building You Can Reach Java Greedy & PriorityQueue

Hard Questions

# Name Solution Algorithm Note
2 Median of Two Sorted Arrays Java Binary Search
10 Regular Expression Matching Java Backtracking
23 Merge k Sorted Lists Java HeapSort
25 Reverse Nodes in k-Group Java LinkedList
30 Substring with Concatenation of All Words Java HashMap
32 Longest Valid Parentheses Java Stack + 1D DP
37 Sudoku Solver Java Backtracking
41 First Missing Positive Java Array
42 Trapping Rain Water Java Greedy/Two-Pointer
44 Wildcard Matching Java Backtracking/Two-Pointer
45 Jump Game II Java 1D DP/Greedy
51 N-Queens Java Backtracking (DFS)
52 N-Queens II Java Backtracking (DFS)
57 Insert Interval Java Sort
65 Valid Number Java String
68 Text Justification Java String
72 Edit Distance Java 2D DP
76 Minimum Window Substring Java Sliding Window
84 Largest Rectangle in Histogram Java Stack
85 Maximal Rectangle Java 2D DP
87 Scramble String Java Backtracking
97 Interleaving String Java 2D DP
99 Recover Binary Search Tree Java Morris Traversal
115 Distinct Subsequences Java 2D DP
123 Best Time to Buy and Sell Stock III Java DP
124 Binary Tree Maximum Path Sum Java DFS
126 Word Ladder II Java Backtracking (DFS + BFS) Both DFS and BFS fail as TLE in OJ
128 Longest Consecutive Sequence Java UnionFind + HashMap
132 Palindrome Partitioning II Java 2D DP
135 Candy Java Greedy
140 Word Break II Java 1D DP + DFS
145 Binary Tree Postorder Traversal Java Stack & Set
149 Max Points on a Line Java HashMap Using double as key in hashmap is generally not a good practice
154 Find Minimum in Rotated Sorted Array II Java Binary Search
164 Maximum Gap Java BucketSort
174 Dungeon Game Java Backtracking (DFS) & DP Backtracking - TLE
212 Word Search II Java Backtracking (DFS) & Trie
214 Shortest Palindrome Java String
224 Basic Calculator Java Stack
239 Sliding Window Maximum Java Deque
265 Paint House II Java 2D DP LintCode 516
269 Alien Dictionary Java Topological Sort LintCode 892 - OJ on LintCode is incorrect
273 Integer to English Words Java String
282 Expression Add Operators Java Backtracking (DFS)
291 Word Pattern II Java Backtracking (DFS) LintCode 829
295 Find Median from Data Stream Java Heap Solution for follow-ups:
1. counting sort between 0 and 100
2. count numbers, which is > 100 and < 0
296 Best Meeting Point Java Math LintCode 912
297 Serialize and Deserialize Binary Tree Java Tree/DFS/Queue
301 Remove Invalid Parentheses Java Backtracking (DFS)
302 Smallest Rectangle Enclosing Black Pixels Java Backtracking (DFS) LintCode 600
305 Number of Islands II Java UnionFind LintCode 434
308 Range Sum Query 2D - Mutable Java Matrix LintCode 817
312 Burst Balloons Java 2D DP
315 Count of Smaller Numbers After Self Java Sort OJ TLE
316 Remove Duplicate Letters Java Greedy
317 Shortest Distance from All Buildings Java BFS LintCode 803
329 Longest Increasing Path in a Matrix Java Backtracking (DFS) DFS with cache
330 Patching Array Java Greedy Cannot be a real interview question
336 Palindrome Pairs Java Trie
340 Longest Substring with At Most K Distinct Characters Java Two-Pointer LintCode 386 as medium
352 Data Stream as Disjoint Intervals Java Binary Search & Union Find
381 Insert Delete GetRandom O(1) - Duplicates allowed Java HashMap
403 Frog Jump Java HashMap
425 Word Squares Java Backtracking (DFS) LintCode 634
432 All O`one Data Structure Java HashMap + DoublyLinkedList
440 K-th Smallest in Lexicographical Order Java Tree
460 LFU Cache Java HashMap + DoublyLinkedList
480 Sliding Window Median Java Heap
546 Remove Boxes Java Backtracking (DFS) Backtracking is TLE. 3D DP solution is here
778 Swim in Rising Water Java Backtracking (DFS) + UnionFind
815 Bus Routes Java Graph Traversal (BFS + DFS)
980 Unique Paths III Java Backtracking (DFS)

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