LeetCode树专题 98. 验证二叉搜索树 二叉搜索树,每个结点的值都有一个范围 /** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ class Solution { public: bool isVal…

树的测试框架: // leetcodeTree.cpp : 定义控制台应用程序的入口点. // #include "stdafx.h" #include <iostream> #include <queue> #include <stack> #include <vector> using namespace std; struct TreeNode { int val; TreeNode *left; TreeNode *right;…

1. sum-root-to-leaf-numbers Given a binary tree containing digits from0-9only, each root-to-leaf path could represent a number. An example is the root-to-leaf path1->2->3which represents the number123. Find the total sum of all root-to-leaf numbers.…

均为 Simple 难度的水题. 二叉树的中序遍历 题目[94]:给定一个二叉树,返回它的中序 遍历. 解题思路:Too simple. class Solution { public: vector<int> inorderTraversal(TreeNode *root) { return inorderNonRec(root); vector<int> v; innerTraversal(root, v); return v; } void innerTraversal(Tr…

637: 二叉树的层平均值 给定一个非空二叉树,返回一个由每层节点平均值组成的数组: https://leetcode-cn.com/problems/average-of-levels-in-binary-tree/   class Solution(object): def averageOfLevels(self, root): """ :type root: TreeNode :rtype: List[float] 实现方法: 设置两个数组,一个用于记录每层树的总和,…

满二叉树是一类二叉树,其中每个结点恰好有 0 或 2 个子结点. 返回包含 N 个结点的所有可能满二叉树的列表. 答案的每个元素都是一个可能树的根结点. 答案中每个树的每个结点都必须有 node.val=0. 你可以按任何顺序返回树的最终列表. 示例: 输入:7 输出:[[0,0,0,null,null,0,0,null,null,0,0],[0,0,0,null,null,0,0,0,0],[0,0,0,0,0,0,0],[0,0,0,0,0,null,null,null,null,0,0],…

二叉树的锯齿形层次遍历     给定一个二叉树,返回其节点值的锯齿形层次遍历.(即先从左往右,再从右往左进行下一层遍历,以此类推,层与层之间交替进行). 例如:给定二叉树 [3,9,20,null,null,15,7], 3 / \ 9 20 / \ 15 7 返回锯齿形层次遍历如下: [ [3], [20,9], [15,7] ] 我的想法是把树的每一层存起来,然后 技术层次的结点顺序翻转一下 # Definition for a binary tree node. # class TreeN…

All questions are simple level. Construct String from Binary Tree Question[606]:You need to construct a string consists of parenthesis and integers from a binary tree with the preorder traversing way. The null node needs to be represented by empty pa…

本文为senlie原创,转载请保留此地址:http://blog.csdn.net/zhengsenlie Populating Next Right Pointers in Each Node II Total Accepted: 9695 Total Submissions: 32965 Follow up for problem "Populating Next Right Pointers in Each Node". What if the given tree could…

目录 144前序遍历 94中序遍历(98验证二叉搜索树.230二叉搜索树中第K小的元素) 145后序遍历 102/107层次遍历(104二叉树最大深度.103 105从前序与中序遍历序列构造二叉树 114二叉树展开为链表 124二叉树中的最大路径和 235/236二叉树的最近公共祖先 144前序遍历 思路:(循环前入栈.先右节点入栈) 建栈,入栈,循环,只要栈不为空 出栈,把值加入res. 如果右不为空,入栈.左一样. List<Integer> res = new ArrayList<…

208. Implement Trie (Prefix Tree) 子节点个数对应的是数组…

我的春招 Hello,首先自我介绍一下,我是一所普普通通的二本院校的大三学生,坐标江苏. 今年三月份拿到了腾讯实习的offer,人生中第一次面试是腾讯,部门是 TEG 的云架构,并且顺利签约,说实话内心还是挺高兴的,在这里和大家分享一下自己的经历. 该读者后面也拿到了阿里的 offer 我的看法 下手要果断.不要怕自己不够好不够强,我大概是二月底开始投简历.我一开始使用了牛客网投简历的方式,很遗憾,记得牛客网公众号当时给我的等待面试安排直到现在我都没有收到安排,效率过慢,很容易失去机会.不过我的…

For a undirected graph with tree characteristics, we can choose any node as the root. The result graph is then a rooted tree. Among all possible rooted trees, those with minimum height are called minimum height trees (MHTs). Given such a graph, write…

Given n nodes labeled from 0 to n - 1 and a list of undirected edges (each edge is a pair of nodes), write a function to check whether these edges make up a valid tree. For example: Given n = 5 and edges = [[0, 1], [0, 2], [0, 3], [1, 4]], return tru…

Implement a trie with insert, search, and startsWith methods. Note:You may assume that all inputs are consist of lowercase letters a-z. 这道题让我们实现一个重要但又有些复杂的数据结构-字典树, 又称前缀树或单词查找树,详细介绍可以参见网友董的博客,例如,一个保存了8个键的trie结构,"A", "to", "tea&quo…

Given two binary trees, write a function to check if they are equal or not. Two binary trees are considered equal if they are structurally identical and the nodes have the same value. 判断两棵树是否相同和之前的判断两棵树是否对称都是一样的原理,利用深度优先搜索DFS来递归.代码如下: 解法一: class Solu…

题目:Symmetric Tree <span style="font-size:18px;"><span style="font-size:18px;">/**LeetCode Symmetric Tree 对称的树 * 思路:推断一棵树是否对称,1.有左子树就要有右子树 * 2.除根节点外对称节点值要同样 * 注意:对称后就是左子树的左节点和右子树的右节点比較 * Definition for binary tree * public c…

树的性质推断是树的数据结构比較主要的操作,一般考到都属于非常easy的题目,也就是第一道入门题.面试中最好不能有问题,力求一遍写对.不要给面试官不论什么挑刺机会.LeetCode中关于树的性质有下面题目:Maximum Depth of Binary TreeMinimum Depth of Binary TreeBalanced Binary TreeSame TreeSymmetric Tree 首先说说关于求树的深度的题目,最简单的是求最大深度Maximum Depth of Binary…

leetcode 105题,由树的前序序列和中序序列构建树结构.详细解答参考<剑指offer>page56. 先序遍历结果的第一个节点为根节点,在中序遍历结果中找到根节点的位置.然后就可以将问题拆分,递归求解. /** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(N…

Given two non-empty binary trees s and t, check whether tree t has exactly the same structure and node values with a subtree of s. A subtree of s is a tree consists of a node in s and all of this node's descendants. The tree s could also be considere…

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). For example, this binary tree [1,2,2,3,4,4,3] is symmetric: 1 / \ 2 2 / \ / \ 3 4 4 3 But the following [1,2,2,null,3,null,3] is not: 1 / \ 2 2 \ \ 3 3 Not…

You are asked to cut off trees in a forest for a golf event. The forest is represented as a non-negative 2D map, in this map: 0 represents the obstacle can't be reached. 1 represents the ground can be walked through. The place with number bigger than…

Given a binary tree with n nodes, your task is to check if it's possible to partition the tree to two trees which have the equal sum of values after removing exactly one edge on the original tree. Example 1: Input: 5 / \ 10 10 / \ 2 3 Output: True Ex…

Given a binary tree, return all duplicate subtrees. For each kind of duplicate subtrees, you only need to return the root node of any oneof them. Two trees are duplicate if they have the same structure with same node values. Example 1: 1 / \ 2 3 / /…

Given two non-empty binary trees s and t, check whether tree t has exactly the same structure and node values with a subtree of s. A subtree of s is a tree consists of a node in s and all of this node's descendants. The tree scould also be considered…

Given a binary tree, find the leftmost value in the last row of the tree. Example 1: Input: 2 / \ 1 3 Output: 1 Example 2: Input: 1 / \ 2 3 / / \ 4 5 6 / 7 Output: 7 Note: You may assume the tree (i.e., the given root node) is not NULL. 这道题让我们求二叉树的最左…

与第二章类似,LeetCode指定了TreeNode实现.为了方便后续习题的编写和测试,创建一个基础父类,包含TreeNode实现,以及create()和print()创建和打印树的方法.其中create()采用类似"堆"的方式,用数组表示树形结构,复习一下,左右子结点就是2*i和2*i+1.而print()方法采用前序遍历的方式,通过额外一个参数level确定当前结点的深度,从而打印一些制表符或其他符号来表示出结点的父子关系.两个核心方法都使用递归的方式,实现起来非常简洁! 注:实现…

题目大意 #!/usr/bin/env python # coding=utf-8 # Date: 2018-08-30 """ https://leetcode.com/problems/symmetric-tree/description/ 101. Symmetric Tree Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). Fo…

树的求和属于树的题目中比較常见的,由于能够有几种变体,灵活度比較高,也能够考察到对于树的数据结构和递归的理解. 一般来说这些题目就不用考虑非递归的解法了(尽管事实上道理是跟LeetCode总结 -- 树的遍历篇一样的.仅仅要掌握了应该没问题哈). LeetCode中关于树的求和有下面题目:Path SumPath Sum IISum Root to Leaf NumbersBinary Tree Maximum Path Sum 我们先来看看最常见的题目Path Sum.这道题是推断是否存在从根…

本文原题: LeetCode. 给定 n, 求解独特二叉搜寻树 (binary search trees) 的个数. 什么是二叉搜寻树? 二叉查找树(Binary Search Tree),或者是一棵空树,或者是具有下列性质的二叉树: 若它的左子树不空,则左子树上所有结点的值均小于它的根结点的值: 若它的右子树不空,则右子树上所有结点的值均大于它的根结点的值: 它的左.右子树也分别为二叉排序树. 举个栗子,给定 n = 3, 共有 5 个. 1 3 3 2 1 \ / / / \ \ 3 2 1…