【Symmetric Tree】cpp

题目：

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

For example, this binary tree is symmetric:

But the following is not:

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

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

代码：

/**

 * 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) {

            if (!root) return true;

            stack<TreeNode *> staL, staR;

            staL.push(root->left);

            staR.push(root->right);

            while ( !staL.empty() && !staR.empty() )

            {

                TreeNode *tmpL = staL.top();

                staL.pop();

                TreeNode *tmpR = staR.top();

                staR.pop();

                if ( !tmpL && !tmpR ) continue;

                if ( !tmpL || !tmpR ) return false;

                if ( tmpL->val != tmpR->val ) return false;

                staL.push(tmpL->right);

                staL.push(tmpL->left);

                staR.push(tmpR->left);

                staR.push(tmpR->right);

            }

            return staL.empty() && staR.empty();

    }

};

tips：

深搜思想。设立两个栈：左栈和右栈。

从根节点开始：左子树用左栈遍历（node->left->right）；右子树用右栈遍历(node->right->left)。

这样就可以转化为Same Tree这道题了（http://www.cnblogs.com/xbf9xbf/p/4505032.html）

巴特西

【Symmetric Tree】cpp

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