LeetCode 100. Same Tree

原题链接在这里：https://leetcode.com/problems/same-tree/

题目：

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.

题解：

树的题目多用递归可以简单地写出来。

终止条件：若左右都为空就return true; 若一个为空另一个不为空 return false; 最后两个都不为空时，值不同return false.

Time Complexity: O(n), n是tree的node数目. Space O(logn).

AC Java:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if(p == null && q == null){
            return true;
        }
        if(p == null || q == null){
            return false;
        }
        if(p.val != q.val){
            return false;
        }
        return isSameTree(p.left,q.left) && isSameTree(p.right,q.right);
    }
}

AC JavaScript:

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} p
 * @param {TreeNode} q
 * @return {boolean}
 */
var isSameTree = function(p, q) {
    if(!p || !q){
        return !p && !q;
    }
    
    return p.val == q.val && isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
};

跟上Symmetric Tree, Subtree of Another Tree.