LeetCode: Balanced Binary Tree 解题报告

 1 // Solution 1:
 2     public boolean isBalanced1(TreeNode root) {
 3         return dfs(root).isBalanced;
 4     }
 5     
 6     // bug 1: inner class is like:  "public class ReturnType {", no ()
 7     public class ReturnType {
 8         boolean isBalanced;
 9         int depth;
10         
11         ReturnType(int depth, boolean isBalanced) {
12             this.depth = depth;
13             this.isBalanced = isBalanced;
14         }
15     }
16     
17     public ReturnType dfs(TreeNode root) {
18         ReturnType ret = new ReturnType(0, true);
19         
20         if (root == null) {
21             return ret;
22         }
23         
24         ReturnType left = dfs(root.left);
25         ReturnType right = dfs(root.right);
26         
27         ret.isBalanced = left.isBalanced 
28                          && right.isBalanced 
29                          && Math.abs(left.depth - right.depth) <= 1;
30                          
31         // bug 2: remember to add 1( the root depth )                 
32         ret.depth = Math.max(left.depth, right.depth) + 1;
33         
34         return ret;
35     }

 1 // Solution 2:
 2     public boolean isBalanced(TreeNode root) {
 3         if (root == null) {
 4             return true;
 5         }        
 6         
 7         return isBalanced(root.left) && isBalanced(root.right)
 8             && Math.abs(getDepth(root.left) - getDepth(root.right)) <= 1;
 9     }
10     
11     public int getDepth(TreeNode root) {
12         if (root == null) {
13             return 0;
14         }
15         
16         return Math.max(getDepth(root.left), getDepth(root.right)) + 1;
17     }