[Leetcode][Tree][Symmetric Tree]

 1 /**
 2  * Definition for binary tree
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     bool symmetric(TreeNode * leftnode, TreeNode * rightnode) {
13         if (leftnode == NULL && rightnode == NULL) {
14             return true;
15         }
16         if (leftnode == NULL || rightnode == NULL) {
17             return false;
18         }
19         if (leftnode->val != rightnode->val) {
20             return false;
21         }
22         return symmetric(leftnode->left, rightnode->right) &&
23                symmetric(leftnode->right, rightnode->left);
24     }
25     bool isSymmetric(TreeNode *root) {
26         if (root == NULL) {
27             return true;
28         } else {
29             return symmetric(root->left, root->right);
30         }
31     }
32 };

 1 /**
 2  * Definition for binary tree
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     bool isSymmetric(TreeNode *root) {
13         queue<TreeNode *> q;
14         if (root == NULL) {
15             return true;
16         } else {
17             q.push(root->left);
18             q.push(root->right);
19         }
20         while (!q.empty()) {
21             TreeNode * n1 = q.front();
22             q.pop();
23             TreeNode * n2 = q.front();
24             q.pop();
25             if (n1 == NULL && n2 == NULL) {
26                 continue;
27             }
28             if (n1 == NULL || n2 == NULL) {
29                 return false;
30             }
31             if (n1->val != n2->val) {
32                 return false;
33             }
34             q.push(n1->left);
35             q.push(n2->right);
36             q.push(n1->right);
37             q.push(n2->left);
38         }
39         return true;
40     }
41 };