[leetcode] 101. Symmetric Tree 解题报告

题目链接：https://leetcode.com/problems/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

思路：将左子树先遍历左子树，右子树先遍历右子树，看其是否相等即可！要注意判空！

代码如下:

/**
 * 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 isMorror(TreeNode* left, TreeNode* right)
    {
        if(!left && !right) return true;
        if(!left ^ !right || (left->val != right->val)) return false;
        return isMorror(left->left,right->right) &&isMorror(left->right,right->left);
    }
    bool isSymmetric(TreeNode* root) {
        if(!root) return true;
        return isMorror(root->left, root->right);
    }
};