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RSS订阅原创 199. 二叉树的右视图
给定一棵二叉树，想象自己站在它的右侧，按照从顶部到底部的顺序，返回从右侧所能看到的节点值。示例:输入: [1,2,3,null,5,null,4]输出: [1, 3, 4]解释:1 <—/ 2 3 <—\ 5 4 <—两种方法，bfs和dfsbfs：//bfs/** * Definition for a binary tree node. * struct TreeNode {
2020-05-27 17:21:16
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原创 78. 子集
给定一组不含重复元素的整数数组 nums，返回该数组所有可能的子集（幂集）。说明：解集不能包含重复的子集。示例:输入: nums = [1,2,3]输出:[[3],[1],[2],[1,2,3],[1,3],[2,3],[1,2],[]]方法一：动态规划//动态规划class Solution {public: vector<vector<int>> subsets(vector<int>& nums) {
2020-05-11 20:48:35
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原创 53. 最大子序和
给定一个整数数组 nums ，找到一个具有最大和的连续子数组（子数组最少包含一个元素），返回其最大和。示例:输入: [-2,1,-3,4,-1,2,1,-5,4],输出: 6解释: 连续子数组 [4,-1,2,1] 的和最大，为 6。进阶:如果你已经实现复杂度为 O(n) 的解法，尝试使用更为精妙的分治法求解。方法一：dpclass Solution {public: int maxSubArray(vector<int>& nums) { in
2020-05-11 16:52:33
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原创 148. 排序链表
在 O(n log n) 时间复杂度和常数级空间复杂度下，对链表进行排序。示例 1:输入: 4->2->1->3输出: 1->2->3->4示例 2:输入: -1->5->3->4->0输出: -1->0->3->4->5用归并排序解决，归并排序有两种写法，所以有两种方法。方法一：（迭代的归并排序）...
2020-05-07 15:29:51
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原创 557. 反转字符串中的单词 III
给定一个字符串，你需要反转字符串中每个单词的字符顺序，同时仍保留空格和单词的初始顺序。示例 1:输入: “Let’s take LeetCode contest”输出: “s’teL ekat edoCteeL tsetnoc”注意：在字符串中，每个单词由单个空格分隔，并且字符串中不会有任何额外的空格。方法一：（istringstream）//istringstream对象可以绑定一行...
2020-05-06 16:53:50
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原创 231. 2的幂
给定一个整数，编写一个函数来判断它是否是 2 的幂次方。示例 1:输入: 1输出: true解释: 20 = 1示例 2:输入: 16输出: true解释: 24 = 16示例 3:输入: 218输出: false方法一：log函数：若底数为m，则为log(n)/log(m)pow函数： pow(2,3)=2^3round: 四舍五入取整class Solution...
2020-05-05 17:21:36
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原创 leetcode 19. 删除链表的倒数第N个节点
给定一个链表，删除链表的倒数第 n 个节点，并且返回链表的头结点。示例：给定一个链表: 1->2->3->4->5, 和 n = 2.当删除了倒数第二个节点后，链表变为 1->2->3->5.说明：给定的 n 保证是有效的。进阶：你能尝试使用一趟扫描实现吗？使用快慢指针方法一：//快慢指针/** * Definition for ...
2020-04-27 16:52:11
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原创 leetcode 3. 无重复字符的最长子串
给定一个字符串，请你找出其中不含有重复字符的 最长子串 的长度。示例 1:输入: “abcabcbb”输出: 3解释: 因为无重复字符的最长子串是 “abc”，所以其长度为 3。示例 2:输入: “bbbbb”输出: 1解释: 因为无重复字符的最长子串是 “b”，所以其长度为 1。示例 3:输入: “pwwkew”输出: 3解释: 因为无重复字符的最长子串是 “wke”，所...
2020-04-27 15:49:01
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原创 pat树问题总结2 dfs，bfs
目录根据前中后三种遍历构建树dfs，bfs堆。结合dfs、完全二叉树的一些性质注：dfs写出路径的一般写法，先写出边界条件，在此条件下输出保存路径的数组，然后通过下面所示的方法，将路径的index放入保存路径的数组，并递归。（结合A1053和A1155）（A1053）给出树的结构和权值，找出从根节点到叶子结点路径上权值相加之和等于给定数字的路径，并且从大到小输出路径。分析：模板题。...
2019-07-26 17:32:53
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原创 pat树问题总结3 建树
并不是说其他题不用建树，只是这类题是真正用一个build函数建。其实要看他们的输入，一般来说都会给出二叉树所有结点的data。（A1115）输出一个二叉搜索树最后两层的结点个数a和b，以及他们的和c ：“a + b = c”点评：build一棵二叉树，dfs确认其深度及每层结点个数，最后按要求加和即可。#include <iostream>#include <vector...
2019-07-26 16:39:39
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原创 pat树问题总结1 根据前中后三种遍历构建树
目录根据前中后三种遍历构建树dfs，bfs堆。结合dfs、完全二叉树的一些性质(A1120) 给出一棵二叉树的前序遍历和中序遍历，求这棵树的层序遍历。分析：模板题。#include<iostream>#include<vector>#include<string>#include<queue>#include<algor...
2019-07-24 17:18:59
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原创 动态规划问题
目录动态规划的递归写法和递推写法典型例题总结1.动态规划的递归写法和递推写法1.1 动态规划的递归算法以斐波那契数列为例，用一般的递归写法写出如下代码：int F(int n){ if(n==0||n==1) return 1; else return F(n-1)+F(n-2);}但上面代码会产生许多的重复计算，为了避免重复计算，可以新开一个一维数组dp，用来保存已经...
2019-06-17 16:09:31
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原创 并查集
目录并查集的定义并查集的基本操作路径压缩例题1.并查集的定义并查集，顾名思义：Union,Find,Set. 即支持两个操作：合并和查找。并查集如何实现呢？其实就是一个数组int father[N];,其中father[i]表示元素i的父亲结点，而父亲结点本身就是这个集合内的元素。举个例子，如father[1]=2就是说元素1的父亲为2,。另外，当father[i]==i时，则说...
2019-06-05 17:10:59
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原创 图算法知识点和模板（未完待续）
目录图的储存（邻接表和邻接矩阵）图的遍历（DFS和BFS）最短路径（Dijkstra算法、Bellman-Ford算法与SPFA算法，Floyd算法）最小生成树（Prim算法，Kruskal算法）拓扑排序关键路径1. 图的储存1.1 邻接矩阵就是一个二维数组G[N][N],当G[i][j]=1时，说明顶点i和顶点j存在边；当当G[i][j]=0时，说明顶点i和顶点j不存在边。...
2019-06-05 15:19:40
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原创 leetcode 300. Longest Increasing Subsequence
Given an unsorted array of integers, find the length of longest increasing subsequence.Example:Input: [10,9,2,5,3,7,101,18]Output: 4Explanation: The longest increasing subsequence is [2,3,7,101], ...
2019-05-14 22:20:59
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原创 leetcode 98. Validate Binary Search Tree
Given a binary tree, determine if it is a valid binary search tree (BST).Assume a BST is defined as follows:The left subtree of a node contains only nodes with keys less than the node’s key.The rig...
2019-05-14 20:18:02
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原创 leetcode 501.Find Mode in Binary Search Tree
Given a binary search tree (BST) with duplicates, find all the mode(s) (the most frequently occurred element) in the given BST.Assume a BST is defined as follows:The left subtree of a node contains ...
2019-05-13 22:24:42
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原创 leetcode 72. Edit Distance 编辑距离（字符串动态规划）
Given two words word1 and word2, find the minimum number of operations required to convert word1 to word2.You have the following 3 operations permitted on a word:Insert a characterDelete a characte...
2019-05-12 22:27:57
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原创 leetcode 230. Kth Smallest Element in a BST
Given a binary search tree, write a function kthSmallest to find the kth smallest element in it.Note:You may assume k is always valid, 1 ≤ k ≤ BST’s total elements.Example 1:Input: root = [3,1,4,n...
2019-05-12 16:56:30
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原创 236. Lowest Common Ancestor of a Binary Tree
Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p a...
2019-05-12 16:06:29
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原创 leetcode 455. Assign Cookies
Assume you are an awesome parent and want to give your children some cookies. But, you should give each child at most one cookie. Each child i has a greed factor gi, which is the minimum size of a coo...
2019-05-11 17:19:32
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原创 leetcode 96. Unique Binary Search Trees （好题）
Given n, how many structurally unique BST’s (binary search trees) that store values 1 … n?Example:Input: 3Output: 5Explanation:Given n = 3, there are a total of 5 unique BST’s:1 3 3 ...
2019-05-11 16:56:24
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原创 leetcode 174. Dungeon Game (动态规划经典题)
The demons had captured the princess § and imprisoned her in the bottom-right corner of a dungeon. The dungeon consists of M x N rooms laid out in a 2D grid. Our valiant knight (K) was initially posit...
2019-05-09 21:32:20
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原创 leetcode 64. Minimum Path Sum
Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path.Note: You can only move either down or right at an...
2019-05-09 20:24:40
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原创 leetcode 120.triangle（动态规划经典题）
Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below.For example, given the following triangle[[2],[3,4],[6,5,7],[4,1,8,3]...
2019-05-08 16:52:05
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原创 leetcode 53. Maximum Subarray（动态规划经典题）
Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum.Example:Input: [-2,1,-3,4,-1,2,1,-5,4],Output: 6Explanation:...
2019-05-08 15:33:09
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原创 Leetcode 198. House Robber（动态规划经典题）
You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjacent house...
2019-05-08 15:01:13
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原创 LeetCode 70. Climbing Stairs
You are climbing a stair case. It takes n steps to reach to the top.Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?Note: Given n will be a positive i...
2019-05-07 23:56:33
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原创 leetcode 203.Remove Linked List Elements
Remove all elements from a linked list of integers that have value val.Example:Input: 1->2->6->3->4->5->6, val = 6Output: 1->2->3->4->5大意：移除等于val的元素（可能不止一个）方法：遍历链表，...
2019-05-07 23:38:22
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原创 leetcode 122. Best Time to Buy and Sell Stock II
Say you have an array for which the ith element is the price of a given stock on day i.Design an algorithm to find the maximum profit. You may complete as many transactions as you like (i.e., buy one...
2019-05-07 23:23:14
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原创 leetcode 144. Binary Tree Preorder Traversal
Given a binary tree, return the preorder traversal of its nodes’ values.Example:Input: [1,null,2,3]12/3Output: [1,2,3]Follow up: Recursive solution is trivial, could you do it iteratively?大意...
2019-05-07 23:11:29
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原创 leetcode 114. Flatten Binary Tree to Linked List
Given a binary tree, flatten it to a linked list in-place.For example, given the following tree:1/ 2 5/ \ 3 4 6The flattened tree should look like:123456大意：将二叉树展开为链表方法：有两种展...
2019-05-07 22:54:28
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原创 leetcode 55. Jump Game
Given an array of non-negative integers, you are initially positioned at the first index of the array.Each element in the array represents your maximum jump length at that position.Determine if you ...
2019-05-06 23:27:08
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原创 leetcode 113. Path Sum II
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 ...
2019-05-06 23:14:37
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原创 leetcode112. Path Sum
Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.Note: A leaf is a node with no children.Example:G...
2019-05-06 22:49:08
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原创 leetcode 61. Rotate List
Given a linked list, rotate the list to the right by k places, where k is non-negative.Example 1:Input: 1->2->3->4->5->NULL, k = 2Output: 4->5->1->2->3->NULLExplanati...
2019-05-06 20:36:39
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原创 leetcode92. Reverse Linked List II
Reverse a linked list from position m to n. Do it in one-pass.Note: 1 ≤ m ≤ n ≤ length of list.Example:Input: 1->2->3->4->5->NULL, m = 2, n = 4Output: 1->4->3->2->5->...
2019-05-06 20:19:48
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原创 leetcode206. Reverse Linked List
Reverse a singly linked list.Example:Input: 1->2->3->4->5->NULLOutput: 5->4->3->2->1->NULLFollow up:A linked list can be reversed either iteratively or recursively. ...
2019-05-06 19:39:10
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原创 leetcode 199. Binary Tree Right Side View
Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.Example:Input: [1,2,3,null,5,null,4]Output: [1, 3, 4]E...
2019-05-05 09:55:41
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原创 LeetCode 107. Binary Tree Level Order Traversal II
Given a binary tree, return the bottom-up level order traversal of its nodes’ values. (ie, from left to right, level by level from leaf to root).For example:Given binary tree [3,9,20,null,null,15,7]...
2019-05-05 09:32:33
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