面试题28. 对称的二叉树

[fireairforce]

递归:

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