leetcode_108

题目来源:https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/

思路：
我最开始是想从子节点往根节点做，后来发现，太困难了，好像用不了递归（因为节点命名的原因），所以还是乖乖从根节点往下做。

常规思维：找中点，二分法

代码：
/**

• Definition for a binary tree node.
• public class TreeNode {
• int val;
• TreeNode left;
• TreeNode right;
• TreeNode(int x) { val = x; }

• }
  */
  class Solution {
  public TreeNode sortedArrayToBST(int[] nums) {

   if(nums.length == 0){
       return null;
   }
  TreeNode head = sorted(nums,0,nums.length-1);
   return head;
  

  }

  public TreeNode sorted(int []nums,int low,int high){

  if(low > high){
      return null;
  }
  int mid = (low+high)/2;
  TreeNode node = new TreeNode(nums[mid]);
  node.left = sorted(nums,low,mid-1);
  node.right = sorted(nums,mid+1,high);
  return node;
  

  }
  }