leetcode 101 Symmetric Tree

Symmetric Tree

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?
> read more on how binary tree is serialized on OJ.

OJ's Binary Tree Serialization:
The serialization of a binary tree follows a level order traversal, where '#' signifies a path terminator where no node exists below.

Here's an example:

1
/ \
2   3
/
4
\
5

The above binary tree is serialized as

"{1,2,3,#,#,4,#,#,5}"

.
代码：

/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* struct TreeNode *left;
* struct TreeNode *right;
* };
*/
bool isSym(struct TreeNode *left, struct TreeNode *right) {
if (left == NULL && right == NULL)
return true;
if (left == NULL || right == NULL)
return false;
if (left->val != right->val)
return false;
return isSym(left->left, right->right)
&& isSym(left->right, right->left);
}

bool isSymmetric(struct TreeNode* root) {
if (root == NULL)
return true;
return isSym(root->left, root->right);
}
原题地址：https://leetcode.com/problems/symmetric-tree/