[leetcode] 147. Insertion Sort List

最新推荐文章于 2022-04-09 13:42:00 发布

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本文介绍了一种使用插入排序算法对链表进行排序的方法。通过一个额外的哑节点简化了处理头结点的过程，实现了链表的有序排列。文章提供了详细的算法步骤和C++代码示例。

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Description

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:

Insertion sort iterates, consuming one input element each repetition, and growing a sorted output list.
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.
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

分析

题目的意思是：用插入排序来对链表排序。

这里用到了一个trick，用了额外变量dummy来实现，这样我们在处理头结点的时候就方便多了。

代码

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* insertionSortList(ListNode* head) {
        ListNode* dummy=new ListNode(-1);
        ListNode* cur;
        while(head){
            ListNode* t=head->next;
            cur=dummy;
            while(cur->next&&cur->next->val<head->val){
                cur=cur->next;
            }
            head->next=cur->next;
            cur->next=head;
            head=t;
        }
        return dummy->next;
    }
};