feat: azl397985856#113 azl397985856#124

Author: luzhipeng

Diff for: README.en.md

@@ -18,7 +18,10 @@ This repository will be divided into four parts for now:
 
 - The third part is [Anki flashcards](https://apps.ankiweb.net) that record the LeetCode problems in a certain way so as to make it easier to remember.
 
-- The fourth part is future plans on content that would be introduced into the above parts.
+- The fourth part is daily problems which held at group chat. we solve just one problem all together, so that
+we can get more feedback, moreover the problems can be drafted to add to the problem solving module.
+
+- The fifth part is future plans on content that would be introduced into the above parts.
 
 > Only when having mastered the basic data structures and algorithms can you solve complex problems easily.
 
@@ -154,6 +157,7 @@ The data structures mainly includes:
 - [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) 🆕 
 - [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)
@@ -190,6 +194,7 @@ The data structures mainly includes:
 - [0023.merge-k-sorted-lists](./problems/23.merge-k-sorted-lists.md)
 - [0032.longest-valid-parentheses](./problems/32.longest-valid-parentheses.md) 🆕
 - [0042.trapping-rain-water](./problems/42.trapping-rain-water.md)
+- [0124.binary-tree-maximum-path-sum](./problems/124.binary-tree-maximum-path-sum.md) 🆕
 - [0128.longest-consecutive-sequence](./problems/128.longest-consecutive-sequence.md) 🆕
 - [0145.binary-tree-postorder-traversal](./problems/145.binary-tree-postorder-traversal.md)
 - [0146.lru-cache](./problems/146.lru-cache.md)
@@ -233,6 +238,12 @@ Latest updated flashcards (only lists the front page):
 
 > problems added：#2 #3 #11
 
+### Daily Problems
+
+- [summary](./daily/)
+
+- [project](https://github.com/azl397985856/leetcode/projects/1)
+
 
 
 ### Future Plans

Diff for: README.md

@@ -154,6 +154,7 @@ leetcode 题解，记录自己的 leetcode 解题之路。
 - [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) 🆕 
 - [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)
@@ -190,6 +191,7 @@ leetcode 题解，记录自己的 leetcode 解题之路。
 - [0023.merge-k-sorted-lists](./problems/23.merge-k-sorted-lists.md)
 - [0032.longest-valid-parentheses](./problems/32.longest-valid-parentheses.md) 🆕
 - [0042.trapping-rain-water](./problems/42.trapping-rain-water.md)
+- [0124.binary-tree-maximum-path-sum](./problems/124.binary-tree-maximum-path-sum.md) 🆕
 - [0128.longest-consecutive-sequence](./problems/128.longest-consecutive-sequence.md) 🆕
 - [0145.binary-tree-postorder-traversal](./problems/145.binary-tree-postorder-traversal.md)
 - [0146.lru-cache](./problems/146.lru-cache.md)

Diff for: assets/drawio/124.binary-tree-maximum-path-sum.drawio

@@ -0,0 +1 @@
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Diff for: assets/problems/124.binary-tree-maximum-path-sum-1.jpg

@@ -0,0 +1,99 @@
+## 题目地址
+https://leetcode.com/problems/path-sum-ii/description/
+
+## 题目描述
+```
+Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.
+
+Note: A leaf is a node with no children.
+
+Example:
+
+Given the below binary tree and sum = 22,
+
+      5
+     / \
+    4   8
+   /   / \
+  11  13  4
+ /  \    / \
+7    2  5   1
+Return:
+
+[
+   [5,4,11,2],
+   [5,8,4,5]
+]
+```
+
+## 思路
+
+这道题目是求集合，并不是`求值`，而是枚举所有可能，因此动态规划不是特别切合，因此我们需要考虑别的方法。
+
+这种题目其实有一个通用的解法，就是回溯法。
+网上也有大神给出了这种回溯法解题的
+[通用写法](https://leetcode.com/problems/combination-sum/discuss/16502/A-general-approach-to-backtracking-questions-in-Java-(Subsets-Permutations-Combination-Sum-Palindrome-Partitioning))，这里的所有的解法使用通用方法解答。
+除了这道题目还有很多其他题目可以用这种通用解法，具体的题目见后方相关题目部分。
+
+我们先来看下通用解法的解题思路，我画了一张图：
+
+![backtrack](../assets/problems/backtrack.png)
+
+通用写法的具体代码见下方代码区。
+
+## 关键点解析
+
+- 回溯法
+- backtrack 解题公式
+
+
+## 代码
+
+```js
+/*
+ * @lc app=leetcode id=113 lang=javascript
+ *
+ * [113] Path Sum II
+ */
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+function backtrack(root, sum, res, tempList) {
+  if (root === null) return;
+  if (root.left === null && root.right === null && sum === root.val)
+    return res.push([...tempList, root.val]);
+
+  tempList.push(root.val);
+  backtrack(root.left, sum - root.val, res, tempList);
+
+  backtrack(root.right, sum - root.val, res, tempList);
+  tempList.pop();
+}
+/**
+ * @param {TreeNode} root
+ * @param {number} sum
+ * @return {number[][]}
+ */
+var pathSum = function(root, sum) {
+  if (root === null) return [];
+  const res = [];
+  backtrack(root, sum, res, []);
+  return res;
+};
+```
+
+## 相关题目
+
+- [39.combination-sum](./39.combination-sum.md)
+- [40.combination-sum-ii](./40.combination-sum-ii.md)
+- [46.permutations](./46.permutations.md)
+- [47.permutations-ii](./47.permutations-ii.md)
+- [78.subsets](./78.subsets.md)
+- [90.subsets-ii](./90.subsets-ii.md)
+- [131.palindrome-partitioning](./131.palindrome-partitioning.md)
+
+

Diff for: assets/problems/124.binary-tree-maximum-path-sum.jpg

@@ -0,0 +1,120 @@
+
+## 题目地址
+https://leetcode.com/problems/binary-tree-maximum-path-sum/description/
+
+## 题目描述
+
+```
+Given a non-empty binary tree, find the maximum path sum.
+
+For this problem, a path is defined as any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The path must contain at least one node and does not need to go through the root.
+
+Example 1:
+
+Input: [1,2,3]
+
+       1
+      / \
+     2   3
+
+Output: 6
+Example 2:
+
+Input: [-10,9,20,null,null,15,7]
+
+   -10
+   / \
+  9  20
+    /  \
+   15   7
+
+Output: 42
+```
+
+## 思路
+
+ 这道题目的path让我误解了，然后浪费了很多时间来解这道题
+ 我觉得leetcode给的demo太少了，不足以让我理解path的概念
+ 因此我这里自己画了一个图，来补充一下，帮助大家理解path的概念，不要像我一样理解错啦。
+
+ 首先是官网给的两个例子：
+
+ ![124.binary-tree-maximum-path-sum](../assets/problems/124.binary-tree-maximum-path-sum.jpg)
+
+  接着是我自己画的一个例子：
+
+ ![124.binary-tree-maximum-path-sum](../assets/problems/124.binary-tree-maximum-path-sum-1.jpg)
+
+大家可以结合上面的demo来继续理解一下path， 除非你理解了path，否则不要往下看。
+
+ 
+ 树的题目，基本都是考察递归思想的。因此我们需要思考如何去定义我们的递归函数，
+ 在这里我定义了一个递归函数，它的功能是，`返回以当前节点为根节点的MathPath`
+ 但是有两个条件:
+ 
+ 1. 第一是跟节点必须选择
+ 2. 第二是左右子树只能选择一个
+
+ 为什么要有这两个条件?
+
+ 我的想法是原问题可以转化为：
+
+ 以每一个节点为根节点，我们分别求出max path，最后计算最大值,因此第一个条件需要满足.
+
+ 对于第二个，由于递归函数子节点的返回值会被父节点使用，因此我们如果两个孩子都选择了
+ 就不符合max path的定义了，这也是我没有理解题意，绕了很大弯子的原因。
+
+
+ 因此我的做法就是不断调用递归函数，然后在调用过程中不断计算和更新max，最后在主函数中将max返回即可。
+
+## 关键点解析
+
+- 递归
+- 理解题目中的path定义
+
+## 代码
+
+```js
+
+
+/*
+ * @lc app=leetcode id=124 lang=javascript
+ *
+ * [124] Binary Tree Maximum Path Sum
+ */
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+function helper(node, payload) {
+  if (node === null) return 0;
+
+  const l = helper(node.left, payload);
+  const r = helper(node.right, payload);
+
+  payload.max = Math.max(
+    node.val + Math.max(0, l) + Math.max(0, r),
+    payload.max
+  );
+
+  return node.val + Math.max(l, r, 0);
+}
+/**
+ * @param {TreeNode} root
+ * @return {number}
+ */
+var maxPathSum = function(root) {
+  if (root === null) return 0;
+  const payload = {
+    max: root.val
+  };
+  helper(root, payload);
+  return payload.max;
+};
+```
+
+## 相关题目
+- [113.path-sum-ii](./113.path-sum-ii.md)

Diff for: problems/113.path-sum-ii.md

@@ -92,4 +92,5 @@ var partition = function(s) {
 - [47.permutations-ii](./47.permutations-ii.md)
 - [78.subsets](./78.subsets.md)
 - [90.subsets-ii](./90.subsets-ii.md)
+- [113.path-sum-ii](./113.path-sum-ii.md)
 

Diff for: problems/124.binary-tree-maximum-path-sum.md

@@ -134,5 +134,6 @@ var combinationSum = function(candidates, target) {
 - [47.permutations-ii](./47.permutations-ii.md)
 - [78.subsets](./78.subsets.md)
 - [90.subsets-ii](./90.subsets-ii.md)
+- [113.path-sum-ii](./113.path-sum-ii.md)
 - [131.palindrome-partitioning](./131.palindrome-partitioning.md)
 

Diff for: problems/131.palindrome-partitioning.md

@@ -138,4 +138,5 @@ var combinationSum2 = function(candidates, target) {
 - [47.permutations-ii](./47.permutations-ii.md)
 - [78.subsets](./78.subsets.md)
 - [90.subsets-ii](./90.subsets-ii.md)
+- [113.path-sum-ii](./113.path-sum-ii.md)
 - [131.palindrome-partitioning](./131.palindrome-partitioning.md)

Diff for: problems/39.combination-sum.md

@@ -102,5 +102,6 @@ var permute = function(nums) {
 - [47.permutations-ii](./47.permutations-ii.md)
 - [78.subsets](./78.subsets.md)
 - [90.subsets-ii](./90.subsets-ii.md)
+- [113.path-sum-ii](./113.path-sum-ii.md)
 - [131.palindrome-partitioning](./131.palindrome-partitioning.md)
 

Diff for: problems/40.combination-sum-ii.md

@@ -104,4 +104,5 @@ var permuteUnique = function(nums) {
 - [46.permutations](./46.permutations.md)
 - [78.subsets](./78.subsets.md)
 - [90.subsets-ii](./90.subsets-ii.md)
+- [113.path-sum-ii](./113.path-sum-ii.md)
 - [131.palindrome-partitioning](./131.palindrome-partitioning.md)

Diff for: problems/46.permutations.md

@@ -112,6 +112,7 @@ var subsets = function(nums) {
 - [46.permutations](./46.permutations.md)
 - [47.permutations-ii](./47.permutations-ii.md)
 - [90.subsets-ii](./90.subsets-ii.md)
+- [113.path-sum-ii](./113.path-sum-ii.md)
 - [131.palindrome-partitioning](./131.palindrome-partitioning.md)
 
 

Diff for: problems/47.permutations-ii.md

@@ -112,6 +112,7 @@ var subsetsWithDup = function(nums) {
 - [46.permutations](./46.permutations.md)
 - [47.permutations-ii](./47.permutations-ii.md)
 - [78.subsets](./78.subsets.md)
+- [113.path-sum-ii](./113.path-sum-ii.md)
 - [131.palindrome-partitioning](./131.palindrome-partitioning.md)