LeetCode OJ - 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

分析：同上一题，递归解决

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