LeetCode——Convert Sorted Array to Binary Search Tree

Description：

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

给一个升序有序的数组，构建一个平衡的二叉查找树。

要平衡就要找中间的数来做头结点，递归构造。

/**
* 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) {

if(nums.length == 0) {
return null;
}

TreeNode root = createBST(nums, 0, nums.length-1);

return root;
}

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

return node;
}
}