101. Symmetric Tree

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:

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

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     bool isSymmetric(TreeNode* root) {
13         TreeNode*left,*right;
14         if(!root)
15             return true;
16         queue<TreeNode*>p,q;
17         p.push(root->left);
18         q.push(root->right);
19         while(!(p.empty()&&q.empty()))
20         {
21             left=p.front();
22             p.pop();
23             right=q.front();
24             q.pop();
25             if(left==NULL&&right==NULL)
26                 continue;
27             if(left==NULL||right==NULL)
28                 return false;
29             if(left->val!=right->val)
30                 return false;
31             p.push(left->left);
32             p.push(left->right);
33             q.push(right->right);
34             q.push(right->left);
35         }
36         return true;
37     }
38 };

这个题用了队列好巧妙的说

posted on 2017-09-23 09:12 王早阅读(66) 评论(0) 编辑收藏举报