剑指Offer——对称的二叉树

 1 /*
 2 struct TreeNode {
 3     int val;
 4     struct TreeNode *left;
 5     struct TreeNode *right;
 6     TreeNode(int x) :
 7             val(x), left(NULL), right(NULL) {
 8     }
 9 };
10 */
11 class Solution {
12 public:
13     bool isSymmetrical(TreeNode* pRoot) {
14         if(pRoot == NULL) return true;
15         return isMirror(pRoot->left, pRoot->right);
16     }
17     bool isMirror(TreeNode* p1, TreeNode* p2) {
18         if(p1 == NULL && p2 == NULL) return true;
19         if(p1 == NULL || p2 == NULL) return false;
20         if(p1->val != p2->val) return false;
21         return isMirror(p1->left, p2->right) && isMirror(p1->right, p2->left);
22     }
23 };