Sort list & insertion sort list (list sorting summary)

Sort list

Sort a linked list inO(NLogN) Time using constant space complexity.

 

Note: Merge Sorting: time O (nlogn) and space O (1). the linked list is split into two parts each time and then merged. Fast sorting (using two pointers)

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */ ListNode* getMid(ListNode *head) {    ListNode *first, *second, *preFirst;    preFirst = first = second = head;    while(second != NULL) {        preFirst = first;        first = first->next;        if(second->next == NULL) break;        second = second->next->next;    }    preFirst->next = NULL;    return first;}void Merge(ListNode *head1, ListNode *head2) {    if(head1->val > head2->val) {int tem = head1->val;head1->val = head2->val;head2->val = tem;}    ListNode *p = head1;    while(p->next != NULL && head2 != NULL) {        if(p->next->val >= head2->val) {            ListNode *q = p->next;            p->next = head2;            head2 = head2->next;            p->next->next = q;            p = p->next;        } else {            p = p->next;        }    }    if(head2 != NULL)        p->next = head2;} void MergeSort(ListNode *head) {    if(head == NULL || head->next == NULL) return;    ListNode *mid = getMid(head);MergeSort(head);MergeSort(mid);    Merge(head, mid);} class Solution {public:    ListNode *sortList(ListNode *head) {       MergeSort(head);       return head;    }};

 

Insertion Sort list

Sort a linked list using insertion sort.

Note: different from the sequence table, you can start from the beginning each time you locate the insert position.

/** * 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 *p, *q;        for(q = head; q != NULL; q = q->next) {            for(p = head; p != q; p = p->next) {                if(p->val >= q->val) {                    int tem = p->val;                    p->val = q->val;                    q->val = tem;                }            }        }        return head;    }};