19.3.2 [LeetCode 100] Symmetric Tree

发布时间：2020-12-14 04:22:44 所属栏目：大数据来源：网络整理

导读：Given a binary tree,check whether it is a mirror of itself (ie,symmetric around its center). For example,this binary tree? [1,2,3,4,3] ?is symmetric: 1 / 2 2 / / 3 4 4 3 ? But the following? [1,null,3] ?is not: 1 / 2 2 3 3 ? Note: Bonu

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

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

    1
   /   2   2
 /  / 3  4 4  3

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

    1
   /   2   2
         3    3

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

 1 class Solution {
 2 public:
 3     bool thesame(TreeNode*l,TreeNode*r){
 4         if(l==NULL&&r==NULL)return true;
 5         else if(l==NULL||r==NULL)return false;
 6         bool same=true;
 7         same&=(l->val==r->val);
 8         if(!same)return false;
 9         same&=thesame(l->left,r->right);
10         if(!same)return false;
11         same&=thesame(l->right,r->left);
12         return same;
13     }
14     bool isSymmetric(TreeNode* root) {
15         if(root==NULL)return true;
16         return thesame(root->left,root->right);
17     }
18 };

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（编辑：李大同）

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