/*
 * @lc app=leetcode.cn id=101 lang=javascript
 *
 * [101] 对称二叉树
 */

// @lc code=start
/**
 * 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) {
    var symmetric = function(p, q) {
        if (p === null || q === null) {
            if (p === q) {
                return true
            } else {
                return false
            }
        }
        if (p.val !== q.val) {
            return false
        }
        if (symmetric(p.left, q.right) && symmetric(p.right, q.left)) {
            return true
        } else {
            return false
        }
    };
    return symmetric(root.left, root.right)
};
// @lc code=end