Convert Sorted List to Binary Search Tree

Description

Given the head of a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

 

Example 1:

Input: head = [-10,-3,0,5,9]
Output: [0,-3,9,-10,null,5]
Explanation: One possible answer is [0,-3,9,-10,null,5], which represents the shown height balanced BST.

Example 2:

Input: head = []
Output: []

Example 3:

Input: head = [0]
Output: [0]

Example 4:

Input: head = [1,3]
Output: [3,1]

 

Constraints:

• The number of nodes in head is in the range [0, 2 * 104].
• -10^5 <= Node.val <= 10^5

Solution(javascript)

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {TreeNode}
 */
const sortedListToBST = function (head) {
  const nodes = []
  while (head) {
    head.left = null
    head.right = null
    nodes.push(head)
    head = head.next
  }
  const aux = (nodes, low, high) => { // eslint-disable-line
    if (low > high) {
      return null
    }
    const middle = Math.floor((low + high) / 2)
    nodes[middle].left = aux(nodes, low, middle - 1)
    nodes[middle].right = aux(nodes, middle + 1, high)
    return nodes[middle]
  }
  return aux(nodes, 0, nodes.length - 1)
}