leetcode: Symmetric Tree

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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
    }
};

leetcode: Symmetric Tree

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原文地址：http://blog.csdn.net/flyljg/article/details/48031249