LeetCode 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:

    1   / \  2   2 / \ / \3  4 4  3

But the following is not:

    1   / \  2   2   \   \   3    3

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

confused what "{1,#,2,3}" means?

 

判断二叉树是否镜像相同。

做两个dfs，一个先左子树，后右子树；另一个先右子树，后左子树。

 

代码：

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {vector<TreeNode*> st1,st2;//中右左dfs、中左右dfs栈public:    bool isSymmetric(TreeNode *root) {TreeNode *tp1,*tp2;        st1.clear();st2.clear();st1.push_back(root);st2.push_back(root);while(!st1.empty())//dfs{tp1=st1.back();st1.pop_back();tp2=st2.back();st2.pop_back();if(tp1==NULL&&tp2==NULL)//比较continue;if(tp1!=NULL&&tp2!=NULL&&tp1->val==tp2->val){st1.push_back(tp1->left);st1.push_back(tp1->right);st2.push_back(tp2->right);st2.push_back(tp2->left);}else//不同时返回return false;}return true;//通过探测    }};