19.3.2 [LeetCode 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:
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.
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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 };
注定失败的战争,也要拼尽全力去打赢它;
就算输,也要输得足够漂亮。