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

But the following [1,2,2,null,3,null,3] is not:

由于这道题data structure是二叉树，所以很容易就能想到递归地求解。所以我写了一个

compareMirror

的函数来判断其对称性。然后对于每一个节点地柜调用该函数即可。

/**
* 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 compareMirror(root->left, root->right);
}

bool compareMirror(TreeNode* ln, TreeNode* rn) {
if (ln != NULL && rn != NULL) {
return ln->val == rn->val && compareMirror(ln->left, rn->right) && compareMirror(ln->right, rn->left);
}
else if (ln == NULL && rn == NULL) return true;
return false;
}
};