feat: #1218

Initiativethinker · Nov 2, 2019 · e6ae6c7 · e6ae6c7
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diff --git a/README.en.md b/README.en.md
@@ -145,14 +145,14 @@ The data structures mainly includes:
 
 - [0002. Add Two Numbers](./problems/2.addTwoNumbers.md)
 - [0003. Longest Substring Without Repeating Characters](./problems/3.longestSubstringWithoutRepeatingCharacters.md)
-- [0005.longest-palindromic-substring](./problems/5.longest-palindromic-substring.md) 🆕
+- [0005.longest-palindromic-substring](./problems/5.longest-palindromic-substring.md)
 - [0011.container-with-most-water](./problems/11.container-with-most-water.md)
 - [0015.3-sum](./problems/15.3-sum.md)
 - [0019. Remove Nth Node From End of List](./problems/19.removeNthNodeFromEndofList.md)
 - [0024. Swap Nodes In Pairs](./problems/24.swapNodesInPairs.md)
-- [0029.divide-two-integers](./problems/29.divide-two-integers.md) 🆕
-- [0031.next-permutation](./problems/31.next-permutation.md) 🆕
-- [0033.search-in-rotated-sorted-array](./problems/33.search-in-rotated-sorted-array.md) 🆕
+- [0029.divide-two-integers](./problems/29.divide-two-integers.md)
+- [0031.next-permutation](./problems/31.next-permutation.md)
+- [0033.search-in-rotated-sorted-array](./problems/33.search-in-rotated-sorted-array.md) 
 - [0039.combination-sum](./problems/39.combination-sum.md)
 - [0040.combination-sum-ii](./problems/40.combination-sum-ii.md)
 - [0046.permutations](./problems/46.permutations.md)
@@ -171,12 +171,12 @@ The data structures mainly includes:
 - [0091.decode-ways](./problems/91.decode-ways.md)
 - [0092.reverse-linked-list-ii](./problems/92.reverse-linked-list-ii.md)
 - [0094.binary-tree-inorder-traversal](./problems/94.binary-tree-inorder-traversal.md)
-- [0098.validate-binary-search-tree](./problems/98.validate-binary-search-tree.md) 🆕 
+- [0098.validate-binary-search-tree](./problems/98.validate-binary-search-tree.md) 
 - [0102.binary-tree-level-order-traversal](./problems/102.binary-tree-level-order-traversal.md)
 - [0103.binary-tree-zigzag-level-order-traversal](./problems/103.binary-tree-zigzag-level-order-traversal.md)
 - [0113.path-sum-ii](./problems/113.path-sum-ii.md)
-- [0129.sum-root-to-leaf-numbers](./problems/129.sum-root-to-leaf-numbers.md) 🆕
-- [0130.surrounded-regions](./problems/130.surrounded-regions.md) 🆕 
+- [0129.sum-root-to-leaf-numbers](./problems/129.sum-root-to-leaf-numbers.md) 
+- [0130.surrounded-regions](./problems/130.surrounded-regions.md) 
 - [0131.palindrome-partitioning](./problems/131.palindrome-partitioning.md)
 - [0139.word-break](./problems/139.word-break.md)
 - [0144.binary-tree-preorder-traversal](./problems/144.binary-tree-preorder-traversal.md)
@@ -188,23 +188,23 @@ The data structures mainly includes:
 - [0208.implement-trie-prefix-tree](./problems/208.implement-trie-prefix-tree.md)
 - [0209.minimum-size-subarray-sum](./problems/209.minimum-size-subarray-sum.md)
 - [0215.kth-largest-element-in-an-array](./problems/215.kth-largest-element-in-an-array.md) 🆕 
-- [0221.maximal-square](./problems/221.maximal-square.md) 🆕 
+- [0221.maximal-square](./problems/221.maximal-square.md) 
 - [0229.majority-element-ii](./problems/229.majority-element-ii.md) 🆕 
 - [0230.kth-smallest-element-in-a-bst](./problems/230.kth-smallest-element-in-a-bst.md)
-- [0236.lowest-common-ancestor-of-a-binary-tree](./problems/236.lowest-common-ancestor-of-a-binary-tree.md)🆕 
+- [0236.lowest-common-ancestor-of-a-binary-tree](./problems/236.lowest-common-ancestor-of-a-binary-tree.md)
 - [0238.product-of-array-except-self](./problems/238.product-of-array-except-self.md)
 - [0240.search-a-2-d-matrix-ii](./problems/240.search-a-2-d-matrix-ii.md)
 - [0279.perfect-squares](./problems/279.perfect-squares.md)
-- [0309.best-time-to-buy-and-sell-stock-with-cooldown](./problems/309.best-time-to-buy-and-sell-stock-with-cooldown.md) 🆕 
+- [0309.best-time-to-buy-and-sell-stock-with-cooldown](./problems/309.best-time-to-buy-and-sell-stock-with-cooldown.md) 
 - [0322.coin-change](./problems/322.coin-change.md)
 - [0328.odd-even-linked-list](./problems/328.odd-even-linked-list.md)
 - [0334.increasing-triplet-subsequence](./problems/334.increasing-triplet-subsequence.md)
 - [0365.water-and-jug-problem](./problems/365.water-and-jug-problem.md)
-- [0378.kth-smallest-element-in-a-sorted-matrix](./problems/378.kth-smallest-element-in-a-sorted-matrix.md) 🆕 
+- [0378.kth-smallest-element-in-a-sorted-matrix](./problems/378.kth-smallest-element-in-a-sorted-matrix.md) 
 - [0416.partition-equal-subset-sum](./problems/416.partition-equal-subset-sum.md)
 - [0445.add-two-numbers-ii](./problems/445.add-two-numbers-ii.md)
 - [0454.4-sum-ii](./problems/454.4-sum-ii.md)
-- [0474.ones-and-zeros](./problems/474.ones-and-zeros-en.md) 🆕
+- [0474.ones-and-zeros](./problems/474.ones-and-zeros-en.md)
 - [0494.target-sum](./problems/494.target-sum.md)
 - [0516.longest-palindromic-subsequence](./problems/516.longest-palindromic-subsequence.md)
 - [0518.coin-change-2](./problems/518.coin-change-2.md)
@@ -214,7 +214,8 @@ The data structures mainly includes:
 - [0877.stone-game](./problems/877.stone-game.md)
 - [0887.super-egg-drop](./problems/887.super-egg-drop.md)
 - [0900.rle-iterator](./problems/900.rle-iterator.md)
-- [1031.maximum-sum-of-two-non-overlapping-subarrays](./problems/1031.maximum-sum-of-two-non-overlapping-subarrays.md) 🆕
+- [1031.maximum-sum-of-two-non-overlapping-subarrays](./problems/1031.maximum-sum-of-two-non-overlapping-subarrays.md)
+- [1218.longest-arithmetic-subsequence-of-given-difference.md](./problems/1218.longest-arithmetic-subsequence-of-given-difference.md) 🆕
 
 #### Hard
 

diff --git a/README.md b/README.md
@@ -158,75 +158,77 @@ leetcode 题解，记录自己的 leetcode 解题之路。
 
 - [0002. Add Two Numbers](./problems/2.addTwoNumbers.md)
 - [0003. Longest Substring Without Repeating Characters](./problems/3.longestSubstringWithoutRepeatingCharacters.md)
-- [0005.longest-palindromic-substring](./problems/5.longest-palindromic-substring.md) 🆕
+- [0005.longest-palindromic-substring](./problems/5.longest-palindromic-substring.md)
 - [0011.container-with-most-water](./problems/11.container-with-most-water.md)
 - [0015.3-sum](./problems/15.3-sum.md)
 - [0019. Remove Nth Node From End of List](./problems/19.removeNthNodeFromEndofList.md)
 - [0024. Swap Nodes In Pairs](./problems/24.swapNodesInPairs.md)
-- [0029.divide-two-integers](./problems/29.divide-two-integers.md) 🆕
-- [0031.next-permutation](./problems/31.next-permutation.md) 🆕
-- [0033.search-in-rotated-sorted-array](./problems/33.search-in-rotated-sorted-array.md) 🆕
+- [0029.divide-two-integers](./problems/29.divide-two-integers.md)
+- [0031.next-permutation](./problems/31.next-permutation.md)
+- [0033.search-in-rotated-sorted-array](./problems/33.search-in-rotated-sorted-array.md) 
 - [0039.combination-sum](./problems/39.combination-sum.md)
 - [0040.combination-sum-ii](./problems/40.combination-sum-ii.md)
 - [0046.permutations](./problems/46.permutations.md)
 - [0047.permutations-ii](./problems/47.permutations-ii.md)
 - [0048.rotate-image](./problems/48.rotate-image.md)
-- [0049.group-anagrams](./problems/49.group-anagrams.md)
+- [0049.group-anagrams](./problems/49.group-anagrams.md) 
 - [0055.jump-game](./problems/55.jump-game.md)
 - [0056.merge-intervals](./problems/56.merge-intervals.md)
 - [0062.unique-paths](./problems/62.unique-paths.md )
 - [0073.set-matrix-zeroes](./problems/73.set-matrix-zeroes.md )
 - [0075.sort-colors](./problems/75.sort-colors.md)
 - [0078.subsets](./problems/78.subsets.md)
-- [0079.word-search](./problems/79.word-search.md)
+- [0079.word-search](./problems/79.word-search-en.md)
 - [0086.partition-list](./problems/86.partition-list.md)
 - [0090.subsets-ii](./problems/90.subsets-ii.md)
 - [0091.decode-ways](./problems/91.decode-ways.md)
 - [0092.reverse-linked-list-ii](./problems/92.reverse-linked-list-ii.md)
 - [0094.binary-tree-inorder-traversal](./problems/94.binary-tree-inorder-traversal.md)
-- [0098.validate-binary-search-tree](./problems/98.validate-binary-search-tree.md) 🆕
+- [0098.validate-binary-search-tree](./problems/98.validate-binary-search-tree.md)  
 - [0102.binary-tree-level-order-traversal](./problems/102.binary-tree-level-order-traversal.md)
 - [0103.binary-tree-zigzag-level-order-traversal](./problems/103.binary-tree-zigzag-level-order-traversal.md)
 - [0113.path-sum-ii](./problems/113.path-sum-ii.md)
-- [0129.sum-root-to-leaf-numbers](./problems/129.sum-root-to-leaf-numbers.md) 🆕
-- [0130.surrounded-regions](./problems/130.surrounded-regions.md) 🆕
+- [0129.sum-root-to-leaf-numbers](./problems/129.sum-root-to-leaf-numbers.md) 
+- [0130.surrounded-regions](./problems/130.surrounded-regions.md) 
 - [0131.palindrome-partitioning](./problems/131.palindrome-partitioning.md)
 - [0139.word-break](./problems/139.word-break.md)
 - [0144.binary-tree-preorder-traversal](./problems/144.binary-tree-preorder-traversal.md)
 - [0150.evaluate-reverse-polish-notation](./problems/150.evaluate-reverse-polish-notation.md)
 - [0152.maximum-product-subarray](./problems/152.maximum-product-subarray.md)
 - [0199.binary-tree-right-side-view](./problems/199.binary-tree-right-side-view.md)
-- [0200.number-of-islands](./problems/200.number-of-islands.md) 🆕
+- [0200.number-of-islands](./problems/200.number-of-islands.md) 🆕 
 - [0201.bitwise-and-of-numbers-range](./problems/201.bitwise-and-of-numbers-range.md)
 - [0208.implement-trie-prefix-tree](./problems/208.implement-trie-prefix-tree.md)
 - [0209.minimum-size-subarray-sum](./problems/209.minimum-size-subarray-sum.md)
-- [0215.kth-largest-element-in-an-array](./problems/215.kth-largest-element-in-an-array.md) 🆕
-- [0221.maximal-square](./problems/221.maximal-square.md) 🆕
-- [0229.majority-element-ii](./problems/229.majority-element-ii.md) 🆕
+- [0215.kth-largest-element-in-an-array](./problems/215.kth-largest-element-in-an-array.md) 🆕 
+- [0221.maximal-square](./problems/221.maximal-square.md) 
+- [0229.majority-element-ii](./problems/229.majority-element-ii.md) 🆕 
 - [0230.kth-smallest-element-in-a-bst](./problems/230.kth-smallest-element-in-a-bst.md)
-- [0236.lowest-common-ancestor-of-a-binary-tree](./problems/236.lowest-common-ancestor-of-a-binary-tree.md)🆕
+- [0236.lowest-common-ancestor-of-a-binary-tree](./problems/236.lowest-common-ancestor-of-a-binary-tree.md)
 - [0238.product-of-array-except-self](./problems/238.product-of-array-except-self.md)
 - [0240.search-a-2-d-matrix-ii](./problems/240.search-a-2-d-matrix-ii.md)
 - [0279.perfect-squares](./problems/279.perfect-squares.md)
-- [0309.best-time-to-buy-and-sell-stock-with-cooldown](./problems/309.best-time-to-buy-and-sell-stock-with-cooldown.md) 🆕
+- [0309.best-time-to-buy-and-sell-stock-with-cooldown](./problems/309.best-time-to-buy-and-sell-stock-with-cooldown.md) 
 - [0322.coin-change](./problems/322.coin-change.md)
 - [0328.odd-even-linked-list](./problems/328.odd-even-linked-list.md)
 - [0334.increasing-triplet-subsequence](./problems/334.increasing-triplet-subsequence.md)
 - [0365.water-and-jug-problem](./problems/365.water-and-jug-problem.md)
-- [0378.kth-smallest-element-in-a-sorted-matrix](./problems/378.kth-smallest-element-in-a-sorted-matrix.md) 🆕
+- [0378.kth-smallest-element-in-a-sorted-matrix](./problems/378.kth-smallest-element-in-a-sorted-matrix.md) 
 - [0416.partition-equal-subset-sum](./problems/416.partition-equal-subset-sum.md)
 - [0445.add-two-numbers-ii](./problems/445.add-two-numbers-ii.md)
 - [0454.4-sum-ii](./problems/454.4-sum-ii.md)
+- [0474.ones-and-zeros](./problems/474.ones-and-zeros-en.md)
 - [0494.target-sum](./problems/494.target-sum.md)
 - [0516.longest-palindromic-subsequence](./problems/516.longest-palindromic-subsequence.md)
 - [0518.coin-change-2](./problems/518.coin-change-2.md)
+- [0547.friend-circles](./problems/547.friend-circles-en.md) 🆕
 - [0609.find-duplicate-file-in-system](./problems/609.find-duplicate-file-in-system.md)
 - [0875.koko-eating-bananas](./problems/875.koko-eating-bananas.md)
 - [0877.stone-game](./problems/877.stone-game.md)
 - [0887.super-egg-drop](./problems/887.super-egg-drop.md)
 - [0900.rle-iterator](./problems/900.rle-iterator.md)
-- [1031.maximum-sum-of-two-non-overlapping-subarrays](./problems/1031.maximum-sum-of-two-non-overlapping-subarrays.md) 🆕
-
+- [1031.maximum-sum-of-two-non-overlapping-subarrays](./problems/1031.maximum-sum-of-two-non-overlapping-subarrays.md)
+- [1218.longest-arithmetic-subsequence-of-given-difference.md](./problems/1218.longest-arithmetic-subsequence-of-given-difference.md) 🆕
 #### 困难难度
 
 - [0004.median-of-two-sorted-array](./problems/4.median-of-two-sorted-array.md) 🆕

diff --git a/problems/1218.longest-arithmetic-subsequence-of-given-difference.md b/problems/1218.longest-arithmetic-subsequence-of-given-difference.md
@@ -0,0 +1,104 @@
+## 题目地址
+
+https://leetcode-cn.com/problems/longest-arithmetic-subsequence-of-given-difference/
+
+## 题目描述
+
+```
+
+给你一个整数数组 arr 和一个整数 difference，请你找出 arr 中所有相邻元素之间的差等于给定 difference 的等差子序列，并返回其中最长的等差子序列的长度。
+
+ 
+
+示例 1：
+
+输入：arr = [1,2,3,4], difference = 1
+输出：4
+解释：最长的等差子序列是 [1,2,3,4]。
+示例 2：
+
+输入：arr = [1,3,5,7], difference = 1
+输出：1
+解释：最长的等差子序列是任意单个元素。
+示例 3：
+
+输入：arr = [1,5,7,8,5,3,4,2,1], difference = -2
+输出：4
+解释：最长的等差子序列是 [7,5,3,1]。
+ 
+
+提示：
+
+1 <= arr.length <= 10^5
+-10^4 <= arr[i], difference <= 10^4
+
+```
+
+## 思路
+
+最直观的思路是双层循环，我们暴力的枚举出以每一个元素为开始元素，以最后元素结尾的的所有情况。很明显这是所有的情况，这就是暴力法的精髓， 很明显这种解法会TLE（超时），不过我们先来看一下代码，顺着这个思维继续思考。
+
+### 暴力法
+
+```python
+ def longestSubsequence(self, arr: List[int], difference: int) -> int:
+ n = len(arr)
+ res = 1
+ for i in range(n):
+ count = 1
+ for j in range(i + 1, n):
+ if arr[i] + difference * count == arr[j]:
+ count += 1
+
+ if count > res:
+ res = count
+
+ return res
+```
+### 动态规划
+
+上面的时间复杂度是O(n^2)， 有没有办法降低到O(n)呢？很容易想到的是空间换时间的解决方案。
+
+我的想法是将`以每一个元素结尾的最长等差子序列的长度`统统存起来，即`dp[num] = maxLen` 这样我们遍历到一个新的元素的时候，就去之前的存储中去找`dp[num - difference]`, 如果找到了，就更新当前的`dp[num] = dp[num - difference] + 1`, 否则就是不进行操作（还是默认值1）。
+
+这种空间换时间的做法的时间和空间复杂度都是O(n)。
+
+
+## 关键点解析
+
+- 将`以每一个元素结尾的最长等差子序列的长度`统统存起来
+
+
+## 代码
+
+```python
+#
+# @lc app=leetcode.cn id=1218 lang=python3
+#
+# [1218] 最长定差子序列
+#
+
+# @lc code=start
+
+
+class Solution:
+
+ # 动态规划
+ def longestSubsequence(self, arr: List[int], difference: int) -> int:
+ n = len(arr)
+ res = 1
+ dp = {}
+ for num in arr:
+ dp[num] = 1
+ if num - difference in dp:
+ dp[num] = dp[num - difference] + 1
+
+ return max(dp.values())
+
+# @lc code=end
+```
+
+## 相关题目
+
+
+