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

深搜+递归

思想：每次将数组中最中间的数作为根节点，然后递归

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode sortedArrayToBST(int[] num) {
        return sortedArrayToBST(num,0,num.length-1);
    }
    
    private TreeNode sortedArrayToBST(int []num,int start,int end){
    	if(start>end||num.length<1) return null;
    	int mid = (start+end)/2;
    	TreeNode tn = new TreeNode(num[mid]);
    	tn.left = sortedArrayToBST(num,start,mid-1);
    	tn.right = sortedArrayToBST(num,mid+1,end);
    	return tn;
    }
}

[LeetCode]Convert Sorted Array to Binary Search Tree