feat: azl397985856#29 azl397985856#48 azl397985856#49 azl397985856#56 azl397985856#98

Author: luzhipeng

Diff for: README.en.md

@@ -128,33 +128,38 @@ The data structures mainly includes:
 - [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) 🆕
 - [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) 🆕 
 - [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 )🆕 
+- [0073.set-matrix-zeroes](./problems/73.set-matrix-zeroes.md )
 - [0075.sort-colors](./problems/75.sort-colors.md)
 - [0078.subsets](./problems/78.subsets.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) 🆕 
 - [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)
 - [0139.word-break](./problems/139.word-breakmd)
 - [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) 🆕  
+- [0152.maximum-product-subarray](./problems/152.maximum-product-subarray.md)
 - [0199.binary-tree-right-side-view](./problems/199.binary-tree-right-side-view.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) 
-- [0230.kth-smallest-element-in-a-bst](./problems/230.kth-smallest-element-in-a-bst.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)🆕 
-- [0238.product-of-array-except-self](./problems/238.product-of-array-except-self.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) 🆕 
@@ -187,8 +192,9 @@ The data structures mainly includes:
 
 ### Summary of Data Structures and Algorithms
 
-- 🖊 [Data Structure](./thinkings/basic-data-structure.md) (Drafts)
-- 🖊 [Binary Tree Traversal](./thinkings/binary-tree-traversal.md)
+- [Data Structure](./thinkings/basic-data-structure.md) (Drafts)
+- [Basic Algorithm](./thinkings/basic-algorithm.md)Drafts
+- [Binary Tree Traversal](./thinkings/binary-tree-traversal.md)
 - [Dynamic Programming](./thinkings/dynamic-programming.md)
 - [Huffman Encode and Run Length Encode](./thinkings/run-length-encode-and-huffman-encode.md)
 - [Bloom Filter](./thinkings/bloom-filter.md)

Diff for: README.md

@@ -126,33 +126,38 @@ leetcode 题解，记录自己的 leetcode 解题之路。
 - [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) 🆕
 - [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) 🆕 
 - [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 )🆕 
+- [0073.set-matrix-zeroes](./problems/73.set-matrix-zeroes.md )
 - [0075.sort-colors](./problems/75.sort-colors.md)
 - [0078.subsets](./problems/78.subsets.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) 🆕 
 - [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)
 - [0139.word-break](./problems/139.word-breakmd)
 - [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) 🆕  
+- [0152.maximum-product-subarray](./problems/152.maximum-product-subarray.md)
 - [0199.binary-tree-right-side-view](./problems/199.binary-tree-right-side-view.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) 
-- [0230.kth-smallest-element-in-a-bst](./problems/230.kth-smallest-element-in-a-bst.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)🆕 
-- [0238.product-of-array-except-self](./problems/238.product-of-array-except-self.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) 🆕 
@@ -183,8 +188,9 @@ leetcode 题解，记录自己的 leetcode 解题之路。
 
 ### 数据结构与算法的总结
 
-- 🖊 [数据结构](./thinkings/basic-data-structure.md)（草稿）
-- 🖊 [二叉树的遍历](./thinkings/binary-tree-traversal.md)
+- [数据结构](./thinkings/basic-data-structure.md)（草稿）
+- [基础算法](./thinkings/basic-algorithm.md)（草稿）
+- [二叉树的遍历](./thinkings/binary-tree-traversal.md)
 - [动态规划](./thinkings/dynamic-programming.md)
 - [哈夫曼编码和游程编码](./thinkings/run-length-encode-and-huffman-encode.md)
 - [布隆过滤器](./thinkings/bloom-filter.md)

Diff for: assets/drawio/29.divide-two-integers.drawio

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Diff for: assets/drawio/48.rotate-image.drawio

@@ -0,0 +1 @@
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Diff for: assets/problems/29.divide-two-integers.png

@@ -0,0 +1,118 @@
+## 题目地址
+https://leetcode.com/problems/divide-two-integers/description/
+
+## 题目描述
+```
+Given two integers dividend and divisor, divide two integers without using multiplication, division and mod operator.
+
+Return the quotient after dividing dividend by divisor.
+
+The integer division should truncate toward zero.
+
+Example 1:
+
+Input: dividend = 10, divisor = 3
+Output: 3
+Example 2:
+
+Input: dividend = 7, divisor = -3
+Output: -2
+Note:
+
+Both dividend and divisor will be 32-bit signed integers.
+The divisor will never be 0.
+Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231,  231 − 1]. For the purpose of this problem, assume that your function returns 231 − 1 when the division result overflows.
+
+```
+
+## 思路
+
+符合直觉的做法是，减数一次一次减去被减数，不断更新差，直到差小于0，我们减了多少次，结果就是多少。
+
+核心代码：
+
+```js
+  let acc = divisor;
+  let count = 0;
+
+  while (dividend - acc >= 0) {
+    acc += divisor;
+    count++;
+  }
+
+  return count;
+
+```
+
+这种做法简单直观，但是性能却比较差. 下面来介绍一种性能更好的方法。
+
+![29.divide-two-integers](../assets/problems/29.divide-two-integers.png)
+
+通过上面这样的分析，我们直到可以使用二分法来解决，性能有很大的提升。
+
+## 关键点解析
+
+- 二分查找
+
+- 正负数的判断中，这样判断更简单。
+
+```js
+const isNegative = dividend > 0 !== divisor > 0;
+```
+
+
+## 代码
+
+```js
+
+
+/*
+ * @lc app=leetcode id=29 lang=javascript
+ *
+ * [29] Divide Two Integers
+ */
+/**
+ * @param {number} dividend
+ * @param {number} divisor
+ * @return {number}
+ */
+var divide = function(dividend, divisor) {
+  if (divisor === 1) return dividend;
+
+  // 这种方法很巧妙，即符号相同则为正，不同则为负
+  const isNegative = dividend > 0 !== divisor > 0;
+
+  const MAX_INTERGER = Math.pow(2, 31);
+
+  const res = helper(Math.abs(dividend), Math.abs(divisor));
+
+  // overflow
+  if (res > MAX_INTERGER - 1 || res < -1 * MAX_INTERGER) {
+    return MAX_INTERGER - 1;
+  }
+
+  return isNegative ? -1 * res : res;
+};
+
+function helper(dividend, divisor) {
+  // 二分法
+  if (dividend <= 0) return 0;
+  if (dividend < divisor) return 0;
+  if (divisor === 1) return dividend;
+
+  let acc = 2 * divisor;
+  let count = 1;
+
+  while (dividend - acc > 0) {
+    acc += acc;
+    count += count;
+  }
+  // 直接使用位移运算，比如acc >> 1会有问题
+  const last = dividend - Math.floor(acc / 2);
+
+  return count + helper(last, divisor);
+}
+```
+
+## 相关题目
+[875.koko-eating-bananas](./875.koko-eating-bananas.md)

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+## 题目地址
+
+https://leetcode.com/problems/rotate-image/description/
+
+## 题目描述
+
+```
+You are given an n x n 2D matrix representing an image.
+
+Rotate the image by 90 degrees (clockwise).
+
+Note:
+
+You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.
+
+Example 1:
+
+Given input matrix =
+[
+  [1,2,3],
+  [4,5,6],
+  [7,8,9]
+],
+
+rotate the input matrix in-place such that it becomes:
+[
+  [7,4,1],
+  [8,5,2],
+  [9,6,3]
+]
+Example 2:
+
+Given input matrix =
+[
+  [ 5, 1, 9,11],
+  [ 2, 4, 8,10],
+  [13, 3, 6, 7],
+  [15,14,12,16]
+],
+
+rotate the input matrix in-place such that it becomes:
+[
+  [15,13, 2, 5],
+  [14, 3, 4, 1],
+  [12, 6, 8, 9],
+  [16, 7,10,11]
+]
+
+```
+
+## 思路
+
+这道题目让我们 in-place，也就说空间复杂度要求 O(1)，如果没有这个限制的话，很简单。
+
+通过观察发现，我们只需要将第 i 行变成第 n - i - 1 列， 因此我们只需要保存一个原有矩阵，然后按照这个规律一个个更新即可。
+
+![48.rotate-image-1](../assets/problems/48.rotate-image-1.png)
+
+代码：
+
+```js
+var rotate = function(matrix) {
+  // 时间复杂度O(n^2) 空间复杂度O(n)
+  const oMatrix = JSON.parse(JSON.stringify(matrix)); // clone
+  const n = oMatrix.length;
+  for (let i = 0; i < n; i++) {
+    for (let j = 0; j < n; j++) {
+      matrix[j][n - i - 1] = oMatrix[i][j];
+    }
+  }
+};
+```
+
+如果要求空间复杂度是O(1)的话，我们可以用一个temp记录即可，这个时候就不能逐个遍历了。
+比如遍历到1的时候，我们把1存到temp，然后更新1的值为7。 1被换到了3的位置，我们再将3存到temp，依次类推。
+但是这种解法写起来比较麻烦，这里我就不写了。
+
+事实上有一个更加巧妙的做法，我们可以巧妙地利用对称轴旋转达到我们的目的，如图，我们先进行一次以对角线为轴的翻转，然后
+再进行一次以水平轴心线为轴的翻转即可。
+
+![48.rotate-image-2](../assets/problems/48.rotate-image-2.png)
+
+这种做法的时间复杂度是O(n^2) ，空间复杂度是O(1)
+
+## 关键点解析
+
+- 矩阵旋转操作
+
+## 代码
+
+```js
+/*
+ * @lc app=leetcode id=48 lang=javascript
+ *
+ * [48] Rotate Image
+ */
+/**
+ * @param {number[][]} matrix
+ * @return {void} Do not return anything, modify matrix in-place instead.
+ */
+var rotate = function(matrix) {
+  // 时间复杂度O(n^2) 空间复杂度O(1)
+
+  // 做法： 先沿着对角线翻转，然后沿着水平线翻转
+  const n = matrix.length;
+  function swap(arr, [i, j], [m, n]) {
+    const temp = arr[i][j];
+    arr[i][j] = arr[m][n];
+    arr[m][n] = temp;
+  }
+  for (let i = 0; i < n - 1; i++) {
+    for (let j = 0; j < n - i; j++) {
+      swap(matrix, [i, j], [n - j - 1, n - i - 1]);
+    }
+  }
+
+  for (let i = 0; i < n / 2; i++) {
+    for (let j = 0; j < n; j++) {
+      swap(matrix, [i, j], [n - i - 1, j]);
+    }
+  }
+};
+```