Convert Sorted Array to Binary Search Tree

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

balanced tree 是指 tree的 min depth 和max depth不超过某个数值（1）。而不是完全二叉树!!!!

 1 /**
 2  * Definition for binary tree
 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 TreeNode sortedArrayToBST(int[] num) {
12         // IMPORTANT: Please reset any member data you declared, as
13         // the same Solution instance will be reused for each test case.
14         return buildTree(num, 0, num.length - 1);
15     }
16     public TreeNode buildTree(int[] num, int s, int e){
17         if(s > e) return null;
18         int mid = (s + e) / 2;
19         TreeNode root = new TreeNode(num[mid]);
20         root.left = buildTree(num, s, mid - 1);
21         root.right = buildTree(num, mid + 1, e);
22         return root;
23     }
24 }

 

posted on 2013-11-16 07:08  Step-BY-Step  阅读(146)  评论(0)  编辑  收藏  举报

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