【LeetCode热题100（39/100）】对称二叉树

题目地址：链接
思路： 使用递归深度优先搜索（DFS）同时遍历左右子树，确保左右子树的结构和节点值对称。

/*** Definition for a binary tree node.* function TreeNode(val, left, right) {*     this.val = (val===undefined ? 0 : val)*     this.left = (left===undefined ? null : left)*     this.right = (right===undefined ? null : right)* }*/
/*** @param {TreeNode} root* @return {boolean}*/
var isSymmetric = function(root) {let ans = false;if(!root) return ans;const dfs = (left, right) => {if(left == null || right == null) return left == right;if(left.val != right.val) return false;return dfs(left.left, right.right) && dfs(left.right, right.left);}ans = dfs(root.left, root.right)return ans;
};