给一个有序数组, 构造一个二叉排序树
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {number[]} nums
* @return {TreeNode}
*/
function sortedArrayToBST(num) {
if (num.length == 0) {
return null;
}
const head = helper(num, 0, num.length - 1);
return head;
}
function helper(num, low, high) {
if (low > high) {
return null;
}
let mid = parseInt((low + high) / 2);
const node = new TreeNode(num[mid]);
node.left = helper(num, low, mid - 1);
node.right = helper(num, mid + 1, high);
return node;
}