Convert Sorted Array to Binary Search Tree

/**
 * definition for a binary tree node.
 * function treenode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {number[]} nums
 * @return {treenode}
 */
var sortedarraytobst = function(nums) {
    if(!nums.length) return null;
    const result = new treenode(nums)
    return result
};

function treenode(nums) {
    if(nums.length){
        const middleindex = math.floor(nums.length/2)
        this.val = nums[middleindex];
        if(middleindex>0){
             this.left =  new treenode(nums.slice(0, middleindex));
        } else {
             this.left =  null
        }
        if(middleindex<nums.length-1){
            this.right = new treenode(nums.slice(middleindex+1));
       } else {
           this.right = null
       }
    } else { return null }
}

上面是将有序数组转为二叉树的代码～

二分查找的速度为o(log n)， 遍历二叉树的速度为o(n)