[LeetCode]Symmetric Tree

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree is symmetric:

    1   / \  2   2 / \ / \3  4 4  3

But the following is not:

    1   / \  2   2   \   \   3    3

/** * Definition for binary tree * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {public boolean isSymmetric(TreeNode root) {if(root == null) return true;return help(root.left,root.right);}private boolean help(TreeNode left, TreeNode right) {if (left == null || right == null){if(left==null&&right==null) return true;else return false;}if (left.left == null && left.right == null && left.val == right.val&& right.left == null && right.right == null)return true;if(help(left.left,right.right)&&help(left.right,right.left)&&left.val==right.val){return true;}else{return false;}}}