leetCode 108.Convert Sorted Array to Binary Search Tree(将排序数组转换为BST) 解题思路和方法

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

思路：将排序数组转换为高度平衡的二叉搜索树。思想是将中间的值作为根节点，然后左右的数组分别为左右子树。递归求解。

代码如下：

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public TreeNode sortedArrayToBST(int[] nums) {
/**
* 高度平衡二叉搜索树
* 指左右子树的高度差不超过1
* 所以每次从中间构造根节点
* 两边构造左右子树
*/
return BST(nums,0,nums.length-1);
}

private TreeNode BST(int[] nums, int i, int j){
if(i > j){
return null;
}
int mid = (j + i + 1)/2;
TreeNode root = new TreeNode(nums[mid]);
root.left = BST(nums,i,mid-1);
root.right = BST(nums,mid+1,j);
return root;
}
}