LeetCode-in-All

148. Sort List

Medium

Given the head of a linked list, return the list after sorting it in ascending order.

Example 1:

Input: head = [4,2,1,3]

Output: [1,2,3,4]

Example 2:

Input: head = [-1,5,3,4,0]

Output: [-1,0,3,4,5]

Example 3:

Input: head = []

Output: []

Constraints:

• The number of nodes in the list is in the range [0, 5 * 104].
• -105 <= Node.val <= 105

Follow up: Can you sort the linked list in O(n logn) time and O(1) memory (i.e. constant space)?

Solution

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var sortList = function(head) {
    let arr = []
    let current = head
    while (current) {
        arr.push(current)
        current = current.next
    }

    arr = arr.sort((a, b) => {
        if (a.val > b.val) {
            return 1
        } else {
            return -1
        }
    })

    const result = arr.reduce((acc, curr) => {
        acc.next = curr
        return acc.next
    }, arr[0])

    if (!result) {
        return null
    }
    result.next = null
    return arr[0]
};

export { sortList }

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