【Leetcode】147. Insertion Sort List（链表实现插入排序）

落日映苍穹つ 2022-02-05 09:51 170阅读 0赞

Sort a linked list using insertion sort.

![Insertion-sort-example-300px.gif][]  
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：

模拟即可。

faster than 98%

/**
     * 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) {
            if(head==NULL) return NULL;
            ListNode* cor_head, *or_head, *or_end;
            
            cor_head = head;
            or_head = head;
            or_end = head;
            
            while(cor_head){
                if(cor_head != or_head){
                    
                    if(or_head == or_end){
                        if(cor_head->val>=or_head->val){
                            or_end = or_end->next;
                            cor_head = cor_head->next;
                        }else{
                            or_head = cor_head;
                            cor_head = cor_head->next;
                            or_head->next = or_end;
                            or_end->next = cor_head;
                        }
                    }else{
                        if(cor_head->val>=or_end->val){
                            //在排列好的后边
                            or_end->next = cor_head;
                            or_end = cor_head;
                            cor_head = cor_head->next;
                        }else if(cor_head->val<=or_head->val){
                            //在排列好的前面
                            or_end->next = cor_head->next;
                            cor_head->next = or_head;
                            or_head = cor_head;
                            cor_head = or_end->next;
                        }else{
                            ListNode *tmp, *p;
                            p = or_head;
                            tmp = or_head->next;
                            while(tmp){
                                if(tmp->val>cor_head->val){
                                    ListNode *tmp_head;
                                    tmp_head = cor_head;
                                    cor_head = cor_head->next;
                                    or_end->next=cor_head;
                                    p->next = tmp_head;
                                    tmp_head->next = tmp;
                                    break;
                                }
                                tmp = tmp->next;
                                p = p->next;
                            }
                        }
                    }
                }else{
                    cor_head = cor_head->next;
                }
            }
            
            or_end->next = NULL;
            
            return or_head;
        }
    };

下面一种方法稍慢

/**
     * 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(INT_MIN);
            
            auto dummy_addr=&dummy;
            
            while(head){
                auto n = head->next;
                auto d =dummy_addr;
                while(d->next and d->next->val < head->val){
                    d = d->next;
                }
                auto dn = d->next;
                head->next = dn;
                d->next = head;
                head = n;
            }
            return dummy.next;
        }
    };

[Insertion-sort-example-300px.gif]: https://upload.wikimedia.org/wikipedia/commons/0/0f/Insertion-sort-example-300px.gif