109. Convert Sorted List to Binary Search Tree

https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree/

JavaScriptPythonGo

/**
 * 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}
 */
function sortedListToBST(head) {
  const vals = []
  while (head) {
    vals.push(head.val)
    head = head.next
  }

  function buildTree(nums, left, right) {
    if (left > right) {
      return null
    }

    const mid = (left + right + 1) / 2 >> 0
    const root = new TreeNode(nums[mid])
    root.left = buildTree(nums, left, mid - 1)
    root.right = buildTree(nums, mid + 1, right)
    return root
  }

  return buildTree(vals, 0, vals.length - 1)
}

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None


class Solution(object):

    def sortedListToBST(self, head):
        """
        :type head: ListNode
        :rtype: TreeNode
        """
        vals = []
        while head:
            vals.append(head.val)
            head = head.next
        return self.buildTree(vals, 0, len(vals) - 1)

    def buildTree(self, nums, left, right):
        if left > right:
            return None

        mid = (left + right + 1) // 2
        root = TreeNode(nums[mid])
        root.left = self.buildTree(nums, left, mid - 1)
        root.right = self.buildTree(nums, mid + 1, right)
        return root

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func sortedListToBST(head *ListNode) *TreeNode {
	var vals []int
	for head != nil {
		vals = append(vals, head.Val)
		head = head.Next
	}
	return buildTree(vals, 0, len(vals)-1)
}

func buildTree(nums []int, left, right int) *TreeNode {
	if left > right {
		return nil
	}

	sum := left + right
	mid := 0
	if sum%2 == 0 {
		mid = sum / 2
	} else {
		mid = (sum + 1) / 2
	}

	root := &TreeNode{Val: nums[mid]}
	root.Left = buildTree(nums, left, mid-1)
	root.Right = buildTree(nums, mid+1, right)

	return root
}

109. Convert Sorted List to Binary Search Tree ​

109. Convert Sorted List to Binary Search Tree