LeetCode刷题（C++）——Symmetric Tree（Easy）

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

/**
* 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;
return isSymmetric(root,root);
}

bool isSymmetric(TreeNode* pRoot1, TreeNode* pRoot2)
{
if(pRoot1==NULL&&pRoot2==NULL)
return true;
if(pRoot1==NULL||pRoot2==NULL)
return false;
if(pRoot1->val!=pRoot2->val)
return false;
return isSymmetric(pRoot1->left,pRoot2->right)&&isSymmetric(pRoot1->right,pRoot2->left);
}
};