[LeetCode101]Symmetric Tree

题目：

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

For example, this binary tree is symmetric:

But the following is not:

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

分类：Tree BFS DFS

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 helper(root->left, root->right);

     }

     bool helper(TreeNode* p, TreeNode* q) {

         if (!p && !q) {

             return true;

         } else if (!p || !q) {

             return false;

         }

         if (p->val != q->val) {

             return false;

         }

         return helper(p->left,q->right) && helper(p->right, q->left);

     }

 };

巴特西

[LeetCode101]Symmetric Tree

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