Symmetric Tree

【题目描述】

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

【思路】
题目还是挺简单的，就不赘述了。

【代码】

recursive solution：

/**
 * 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==NULL) return true;
        TreeNode* leftnode=root->left;
        TreeNode* rightnode=root->right;
        return judge(leftnode,rightnode);
    }
    bool judge(TreeNode* p,TreeNode* q){
        if(p==NULL&&q==NULL) return true;
        else if(p==NULL||q==NULL) return false;
        if(p->val!=q->val) return false;
        else return judge(p->left,q->right)&&judge(p->right,q->left);
    }
};