101. Symmetric Tree/二叉树

题目描述

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

For example, this binary tree [1,2,2,3,4,4,3] is symmetric:

    1
   / \
  2   2
 / \ / \
3  4 4  3

But the following [1,2,2,null,3,null,3] is not:

    1
   / \
  2   2
   \   \
   3    3

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

题目大意

判断一棵树是不是镜像树。

AC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) {
        return isMirror(root,root);
    }
    bool isMirror(TreeNode* t1,TreeNode* t2){
        if(t1==NULL&&t2==NULL) return true;
        else if(t1==NULL||t2==NULL) return false;
        return (t1->val==t2->val)&&isMirror(t1->right,t2->left)&&isMirror(t1->left,t2->right);
    }
};