leetcode 101. 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

/**
* 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)
{
deque<TreeNode*> que;
if(root)
{
que.push_back(root->left);
que.push_back(root->right);
}
while (!que.empty())
{
TreeNode * left = que.front();
TreeNode * right = que.back();
que.pop_front();
que.pop_back();
if (left == NULL && right == NULL)
continue;
else if(left == NULL || right == NULL || left->val != right->val)
return 0;
else
{
que.push_front(left->right);
que.push_front(left->left);
que.push_back(right->left);
que.push_back(right->right);
}
}
return 1;
}
};