LeetCode: 147. Insertion Sort List

题目描述

Sort a linked list using insertion sort.

A graphical example of insertion sort. The partial sorted list (black) initially contains only the first element in the list.
With each iteration one element (red) is removed from the input data and inserted in-place into the sorted list

Algorithm of Insertion Sort:

1. Insertion sort iterates, consuming one input element each repetition, and growing a sorted output list.
2. At each iteration, insertion sort removes one element from the input data, finds the location it belongs within the sorted list, and inserts it there.
3. It repeats until no input elements remain.

Example 1:

Input: 4->2->1->3
Output: 1->2->3->4

Example 2:

Input: -1->5->3->4->0
Output: -1->0->3->4->5

题目大意：对链表进行插入排序

解题思路

新建一个已排序的链表，然后将未排序链表的节点一个一个插入已排序链表中。

AC 代码

/** * Definition for singly-linked list. * struct ListNode { * int val; * ListNode *next; * ListNode(int x) : val(x), next(NULL) {} * }; */
class Solution {
    // 插入操作：将 head 按顺序插入 sortedList，同时将 head 指向其下一个指针
    void insertNode2SortedList(ListNode*& sortedList, ListNode*& head)
    {
        if(sortedList->next == nullptr || sortedList->next->val > head->val)
        {
            ListNode* backNodes = sortedList->next;
            sortedList->next = head;
            head = head->next;
            sortedList->next->next = backNodes;
        }
        else
        {
            insertNode2SortedList(sortedList->next, head);
        }
    }
public:
    ListNode* insertionSortList(ListNode* head) {
        // 新建已排序链表
        ListNode* sortedList = new ListNode(INT_MIN);
        while(head != nullptr)
        {
            // 将未排序链表的节点插入已排序链表中
            insertNode2SortedList(sortedList, head);
        }

        ListNode* ans = sortedList->next;
        delete sortedList;

        return ans;
    }
};