109-Convert-Sorted-List-to-Binary-Search-Tree.js

/* eslint-disable no-undef */
/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {ListNode} head
 * @return {TreeNode}
 */
const sortedListToBST = (head) => {
    const countNodes = (node) => {
        if (!node) return 0;
        return countNodes(node.next) + 1;
    };

    const traverse = (n) => {
        if (n <= 0) return null;

        const left = traverse(Math.floor(n / 2));
        const root = new TreeNode(head.val);

        root.left = left;
        head = head.next;
        root.right = traverse(n - Math.floor(n / 2) - 1);

        return root;
    };

    return traverse(countNodes(head));
};