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 [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.
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) { if(!root) return true; return another(root -> left, root -> right); } bool another(TreeNode* lt, TreeNode* rt) { if(!lt && !rt) return true; if(!lt || !rt) return false; else { if(lt -> val != rt -> val) return false; else return another(lt -> left, rt -> right) && another(lt -> right, rt -> left); } } };
这个写了超级久本来想到之前的一个反转二叉树 反转之后进行比较 但是 WA 掉好几发一直没改过来