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

Note:

Bonus points if you could solve it both recursively and iteratively.

题目描述：

对称树的判断。

代码实现：

/**
* 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 isSymmetric(TreeNode* root) {
return root ? isSymmetric(root->left,root->right) : true;
}
bool isSymmetric(TreeNode *left,TreeNode *right)
{
if(!left && !right) return true;//终止条件
if(!left || !right) return false;//终止条件
return left->val== right->val && isSymmetric(left->left,right->right) && isSymmetric(left->right,right->left);//三方合并
}
};