LeetCode: Balanced Binary Tree

C++

 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     int dfs(TreeNode *root, bool &flag, int cur) {
13         if (!root || !flag) return cur;
14         int leftH = dfs(root->left, flag, cur+1);
15         if (!flag) return cur;
16         int rightH = dfs(root->right, flag, cur+1);
17         if (abs(leftH-rightH) <= 1 && flag) flag = true;
18         else flag = false;
19         return max(leftH, rightH);
20     }
21     bool isBalanced(TreeNode *root) {
22         // Start typing your C/C++ solution below
23         // DO NOT write int main() function
24         if (!root) return true;
25         bool flag = true;
26         if (abs(dfs(root->left, flag, 0)-dfs(root->right, flag, 0)) <= 1 && flag) return true;
27         else return false;
28     }
29 };

Java: Time complexity: O(N), Space complexity: O(LOGN)

 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     public boolean isBalanced(TreeNode root) {
12         return checkHeight(root) != -1;
13     }
14     private int checkHeight(TreeNode root)
15     {
16         if (root == null)
17         {
18             return 0;
19         }
20         int leftHeight = checkHeight(root.left);
21         if (leftHeight == -1)
22         {
23             return -1;
24         }
25         int rightHeight = checkHeight(root.right);
26         if (rightHeight == -1)
27         {
28             return -1;
29         }
30         int heightDiff = Math.abs(leftHeight - rightHeight);
31         if (heightDiff > 1)
32         {
33             return -1;
34         }
35         else
36         {
37             return Math.max(leftHeight, rightHeight) + 1;
38         }
39     }
40 }

posted @ 2013-03-17 18:47 ying_vincent 阅读(176) 评论(0) 收藏举报

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