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

答案

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