[题目] 判断二叉树是否相同. [思路] check函数. p==null并且q==null,返回true;(两边完全匹配) p==null或q==null,返回false;(p.q其中一方更短) p.val==q.val,值相同,继续迭代向左向右遍历check(p.left,q.left)&&check(p.right,q.right); [代码] public boolean check(TreeNode p, TreeNode q){ if(p==null&&q==n…

[题目] 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…

100. 相同的树 100. Same Tree 题目描述 给定两个二叉树,编写一个函数来检验它们是否相同. 如果两个树在结构上相同,并且节点具有相同的值,则认为它们是相同的. 每日一算法2019/5/5Day 2LeetCode100. Same Tree Java 实现 class TreeNode { int val; TreeNode left; TreeNode right; TreeNode(int x) { val = x; } } public class Solution {…

题目描述 给定一个二叉树,检查它是否是镜像对称的. 例如,二叉树 [1,2,2,3,4,4,3] 是对称的. 1 / \ 2 2 / \ / \ 3 4 4 3 但是下面这个 [1,2,2,null,3,null,3] 则不是镜像对称的: 1 / \ 2 2 \ \ 3 3 说明: 如果你可以运用递归和迭代两种方法解决这个问题,会很加分. 解题思路 本题可用递归和迭代两种做法来求解. 递归做法是每次对于对称的两个节点,首先判断是否都为空,若都为空则返回true:否则判断两节点是否相等,若相等则返…

方法一,记录子树的上界和下界,root的左子树一定小于root的值,root的右子树一定大于root的值,然后递归左子树和右子树 public class Solution { public boolean isValidBST(TreeNode root) { return isValid(root, null, null); } public boolean isValid(TreeNode root, Integer min, Integer max) { if(root == null)…

110. Balanced Binary Tree Given a binary tree, determine if it is height-balanced. For this problem, a height-balanced binary tree is defined as: a binary tree in which the depth of the two subtrees of every node never differ by more than 1. Example…

[LeetCode]Minimum Depth of Binary Tree Given a binary tree, find its minimum depth. The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node. 递归和非递归,此提比较简单.广度优先遍历即可.关键之处就在于如何保持访问深度. 下面是4种代码: im…

判断二叉树是否平衡 a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1. 以下解法为什么时间复杂度为O(n)? /** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNod…

Given a binary tree, find its minimum depth. The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node. 给一个二叉树,找出它的最小深度.最小深度是从根节点向下到最近的叶节点的最短路径,就是最短路径的节点个数. 解法1:DFS 解法2: BFS Java: DFS, Time Comp…

Given a binary tree, find all leaves and then remove those leaves. Then repeat the previous steps until the tree is empty. Example:Given binary tree 1 / \ 2 3 / \ 4 5 Returns [4, 5, 3], [2], [1]. Explanation: 1. Remove the leaves [4, 5, 3] from the t…