Leetcode57: 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 a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    bool isMirror(TreeNode* left, TreeNode* right)    {        if(!left && !right)             return true;        if((!left && right) || (!right && left) || (left->val != right->val))            return false;        return isMirror(left->left, right->right) && isMirror(left->right, right->left);    }    bool isSymmetric(TreeNode* root) {        if(root == NULL)            return true;        if(!root->left && !root->right)            return true;        return isMirror(root->left, root->right);    }};