README.md

2046. Sort Linked List Already Sorted Using Absolute Values

English Version

题目描述

Given the head of a singly linked list that is sorted in non-decreasing order using the absolute values of its nodes, return the list sorted in non-decreasing order using the actual values of its nodes.

 

Example 1:

Input: head = [0,2,-5,5,10,-10]
Output: [-10,-5,0,2,5,10]
Explanation:
The list sorted in non-descending order using the absolute values of the nodes is [0,2,-5,5,10,-10].
The list sorted in non-descending order using the actual values is [-10,-5,0,2,5,10].

Example 2:

Input: head = [0,1,2]
Output: [0,1,2]
Explanation:
The linked list is already sorted in non-decreasing order.

Example 3:

Input: head = [1]
Output: [1]
Explanation:
The linked list is already sorted in non-decreasing order.

 

Constraints:

• The number of nodes in the list is the range [1, 105].
• -5000 <= Node.val <= 5000
• head is sorted in non-decreasing order using the absolute value of its nodes.

 

Follow up:

• Can you think of a solution with O(n) time complexity?

解法

先默认第一个点已经排序完毕。然后从第二个点开始，遇到值为负数的节点，采用头插法；非负数，则继续往下遍历即可。

Python3

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def sortLinkedList(self, head: Optional[ListNode]) -> Optional[ListNode]:
        prev, curr = head, head.next
        while curr:
            if curr.val < 0:
                t = curr.next
                prev.next = t
                curr.next = head
                head = curr
                curr = t
            else:
                prev, curr = curr, curr.next
        return head

Java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode sortLinkedList(ListNode head) {
        ListNode prev = head, curr = head.next;
        while (curr != null) {
            if (curr.val < 0) {
                ListNode t = curr.next;
                prev.next = t;
                curr.next = head;
                head = curr;
                curr = t;
            } else {
                prev = curr;
                curr = curr.next;
            }
        }
        return head;
    }
}

C++

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* sortLinkedList(ListNode* head) {
        ListNode* prev = head;
        ListNode* curr = head->next;
        while (curr)
        {
            if (curr->val < 0)
            {
                auto t = curr->next;
                prev->next = t;
                curr->next = head;
                head = curr;
                curr = t;
            }
            else
            {
                prev = curr;
                curr = curr->next;
            }
        }
        return head;
    }
};

Go

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func sortLinkedList(head *ListNode) *ListNode {
	prev, curr := head, head.Next
	for curr != nil {
		if curr.Val < 0 {
			t := curr.Next
			prev.Next = t
			curr.Next = head
			head = curr
			curr = t
		} else {
			prev, curr = curr, curr.Next
		}
	}
	return head
}

...