From 43cee1d82b191f439cb12d6de9bc901cdebbee40 Mon Sep 17 00:00:00 2001 From: CyC2018 <1029579233@qq.com> Date: Fri, 9 Mar 2018 13:14:49 +0800 Subject: [PATCH] auto commit --- notes/Leetcode 题解.md | 182 +++++++++++++++++++++++++++++++++++------ 1 file changed, 159 insertions(+), 23 deletions(-) diff --git a/notes/Leetcode 题解.md b/notes/Leetcode 题解.md index f0636c85..e5d3a5ee 100644 --- a/notes/Leetcode 题解.md +++ b/notes/Leetcode 题解.md @@ -36,7 +36,7 @@ * [哈希表](#哈希表) * [字符串](#字符串) * [数组与矩阵](#数组与矩阵) - * [1\~n 分布](#1\~n-分布) + * [1-n 分布](#1-n-分布) * [有序矩阵](#有序矩阵) * [链表](#链表) * [树](#树) @@ -3472,7 +3472,7 @@ public void moveZeroes(int[] nums) { } ``` -### 1\~n 分布 +### 1-n 分布 **一个数组元素在 [1, n] 之间，其中一个数被替换为另一个数，找出丢失的数和重复的数** @@ -3855,6 +3855,23 @@ public TreeNode invertTree(TreeNode root) { [Leetcode : 617. Merge Two Binary Trees (Easy)](https://leetcode.com/problems/merge-two-binary-trees/description/) +```html +Input: + Tree 1 Tree 2 + 1 2 + / \ / \ + 3 2 1 3 + / \ \ + 5 4 7 +Output: +Merged tree: + 3 + / \ + 4 5 + / \ \ + 5 4 7 +``` + ```java public TreeNode mergeTrees(TreeNode t1, TreeNode t2) { if(t1 == null && t2 == null) return null; @@ -3871,7 +3888,19 @@ public TreeNode mergeTrees(TreeNode t1, TreeNode t2) { [Leetcdoe : 112. Path Sum (Easy)](https://leetcode.com/problems/path-sum/description/) -题目描述：路径和定义为从 root 到 leaf 的所有节点的和 +```html +Given the below binary tree and sum = 22, + 5 + / \ + 4 8 + / / \ + 11 13 4 + / \ \ + 7 2 1 +return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22. +``` + +路径和定义为从 root 到 leaf 的所有节点的和 ```java public boolean hasPathSum(TreeNode root, int sum) { @@ -3885,9 +3914,25 @@ public boolean hasPathSum(TreeNode root, int sum) { [Leetcode : 437. Path Sum III (Easy)](https://leetcode.com/problems/path-sum-iii/description/) -题目描述：路径不一定以 root 开头并以 leaf 结尾，但是必须连续 +```html +root = [10,5,-3,3,2,null,11,3,-2,null,1], sum = 8 -pathSumStartWithRoot() 方法统计以某个节点开头的路径个数。 + 10 + / \ + 5 -3 + / \ \ + 3 2 11 + / \ \ +3 -2 1 + +Return 3. The paths that sum to 8 are: + +1. 5 -> 3 +2. 5 -> 2 -> 1 +3. -3 -> 11 +``` + +路径不一定以 root 开头并以 leaf 结尾，但是必须连续 ```java public int pathSum(TreeNode root, int sum) { @@ -3909,6 +3954,14 @@ private int pathSumStartWithRoot(TreeNode root, int sum){ [Leetcode : 101. Symmetric Tree (Easy)](https://leetcode.com/problems/symmetric-tree/description/) +```html + 1 + / \ + 2 2 + / \ / \ +3 4 4 3 +``` + ```java public boolean isSymmetric(TreeNode root) { if(root == null) return true; @@ -3927,7 +3980,15 @@ private boolean isSymmetric(TreeNode t1, TreeNode t2){ [Leetcode : 110. Balanced Binary Tree (Easy)](https://leetcode.com/problems/balanced-binary-tree/description/) -题目描述：左右子树高度差是否都小于等于 1 +```html + 3 + / \ + 9 20 + / \ + 15 7 +``` + +平衡树左右子树高度差都小于等于 1 ```java private boolean result = true; @@ -3950,7 +4011,7 @@ public int maxDepth(TreeNode root) { [Leetcode : 111. Minimum Depth of Binary Tree (Easy)](https://leetcode.com/problems/minimum-depth-of-binary-tree/description/) -题目描述：树的根节点到叶子节点的最小长度 +树的根节点到叶子节点的最小路径长度 ```java public int minDepth(TreeNode root) { @@ -3966,24 +4027,63 @@ public int minDepth(TreeNode root) { [Leetcode : 404. Sum of Left Leaves (Easy)](https://leetcode.com/problems/sum-of-left-leaves/description/) +```html + 3 + / \ + 9 20 + / \ + 15 7 + +There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24. +``` + ```java public int sumOfLeftLeaves(TreeNode root) { - if(root == null) return 0; - if(isLeaf(root.left)) return root.left.val + sumOfLeftLeaves(root.right); + if(root == null) { + return 0; + } + if(isLeaf(root.left)) { + return root.left.val + sumOfLeftLeaves(root.right); + } return sumOfLeftLeaves(root.left) + sumOfLeftLeaves(root.right); } private boolean isLeaf(TreeNode node){ - if(node == null) return false; + if(node == null) { + return false; + } return node.left == null && node.right == null; } ``` -**修剪一棵树** +**修剪二叉查找树** [Leetcode : 669. Trim a Binary Search Tree (Easy)](https://leetcode.com/problems/trim-a-binary-search-tree/description/) -题目描述：只保留值在 L \~ R 之间的节点 +```html +Input: + 3 + / \ + 0 4 + \ + 2 + / + 1 + + L = 1 + R = 3 + +Output: + 3 + / + 2 + / + 1 +``` + +二叉查找树（BST）：根节点大于等于左子树所有节点，小于等于右子树所有节点。 + +只保留值在 L \~ R 之间的节点 ```java public TreeNode trimBST(TreeNode root, int L, int R) { @@ -4000,6 +4100,20 @@ public TreeNode trimBST(TreeNode root, int L, int R) { [Leetcode : 572. Subtree of Another Tree (Easy)](https://leetcode.com/problems/subtree-of-another-tree/description/) +```html +Given tree s: + 3 + / \ + 4 5 + / \ + 1 2 +Given tree t: + 4 + / \ + 1 2 +Return true, because t has the same structure and node values with a subtree of s. +``` + ```java public boolean isSubtree(TreeNode s, TreeNode t) { if(s == null && t == null) return true; @@ -4020,8 +4134,6 @@ private boolean isSame(TreeNode s, TreeNode t){ [Leetcode : 108. Convert Sorted Array to Binary Search Tree (Easy)](https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/description/) -二叉查找树（BST）：根节点大于等于左子树所有节点，小于等于右子树所有节点。 - ```java public TreeNode sortedArrayToBST(int[] nums) { return toBST(nums, 0, nums.length - 1); @@ -4040,15 +4152,19 @@ private TreeNode toBST(int[] nums, int sIdx, int eIdx){ **两节点的最长路径** ```html - 1 +Input: + + 1 / \ - 2 3 + 2 3 / \ 4 5 Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3]. ``` +[Leetcode : 543. Diameter of Binary Tree (Easy)](https://leetcode.com/problems/diameter-of-binary-tree/description/) + ```java private int max = 0; @@ -4058,9 +4174,7 @@ public int diameterOfBinaryTree(TreeNode root) { } private int depth(TreeNode root) { - if (root == null) { - return 0; - } + if (root == null) return 0; int leftDepth = depth(root.left); int rightDepth = depth(root.right); max = Math.max(max, leftDepth + rightDepth); @@ -4074,9 +4188,9 @@ private int depth(TreeNode root) { ```html Input: - 2 + 2 / \ - 2 5 + 2 5 / \ 5 7 @@ -4099,10 +4213,21 @@ public int findSecondMinimumValue(TreeNode root) { } ``` -**寻找两个节点的最近公共祖先** +**二叉查找树的最近公共祖先** [Leetcode : 235. Lowest Common Ancestor of a Binary Search Tree (Easy)](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/description/) +```html + _______6______ + / \ + ___2__ ___8__ + / \ / \ + 0 _4 7 9 + / \ + 3 5 +For example, the lowest common ancestor (LCA) of nodes 2 and 8 is 6. Another example is LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition. +``` + ```java public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { if(root.val > p.val && root.val > q.val) return lowestCommonAncestor(root.left, p, q); @@ -4111,10 +4236,21 @@ public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { } ``` -**最近公共祖先** +**二叉树的最近公共祖先** [Leetcode : 236. Lowest Common Ancestor of a Binary Tree (Medium) ](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/description/) +```html + _______3______ + / \ + ___5__ ___1__ + / \ / \ + 6 _2 0 8 + / \ + 7 4 +For example, the lowest common ancestor (LCA) of nodes 5 and 1 is 3. Another example is LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition. +``` + ```java public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { if (root == null || root == p || root == q) return root;