链表的基本操作

 链表排序

    二路归并（暂未实现）

    基本思想：维护一个队列，从头便利链表，找到一段按降序排列的链表段，一段一段的分开，然后将它们按顺序入队，每次从对头取出两个进行归并，归并后的结果入队。

#include <iostream>using namespace std;struct node{int d;node *next;node(int x){d = x;next = NULL;}};//链表找中点node *findminnode(node *head){if(head == NULL || head->next == NULL)return head;node *onestep = head;node *twostep = head;while(twostep->next != NULL && twostep->next->next != NULL){onestep = onestep->next;twostep = twostep->next->next;}return onestep;}//两条单链表判断是否相交bool judgexiangjiao(node *head1,node *head2){if(head1 == NULL || head2 == NULL) return 0;node *p1 = head1;node *p2 = head2;while(p1->next != NULL) p1 = p1->next;while(p2->next != NULL) p2 = p2->next;if(p1 == p2) return 1;return 0;}//单链表判断有无环，并输出环的起始点bool ishascycle(node *head,node *&onenode){if(head == NULL || head->next== NULL) return 0;node *onestep = head;node *twostep = head;while(twostep->next != NULL && twostep->next->next != NULL){onestep = onestep->next;twostep = twostep->next->next;if(onestep == twostep){onenode = onestep;return 1;}}return 0;}node * findfirstnode(node *head){node *onenode = NULL;bool isc = ishascycle(head,onenode);if(isc){node * fromhead = head;node * fromonenode = onenode->next;int headcount = 0;int onecount = 0;while(fromhead != onenode){fromhead=fromhead->next;headcount++;}while(fromonenode != onenode){fromonenode = fromonenode->next;onecount++;}int cha = 0;node *fromlong = NULL;node *fromshort = NULL;if(headcount > onecount){cha = headcount - onecount;fromlong = head;fromshort = onenode->next;}else{cha = onecount - headcount;fromshort = head;fromlong = onenode->next;}while(cha--){fromlong = fromlong->next;}while(fromlong != fromshort){fromshort = fromshort->next;fromlong = fromlong->next;}return fromlong;}return NULL;}//链表逆序node *reve(node *head){if(head == NULL ||head->next == NULL) return NULL;node *pre = NULL;node *cur = head;node *nex ;while(cur != NULL){nex = cur->next;cur->next = pre;pre = cur;cur = nex;}return pre;}int main(){node *head = new node(1);node *n2 = new node(2);node *n3 = new node(3);node *n4 = new node(4);node *n5 = new node(5);node *n6 = new node(6);node *n7 = new node(7);node *n8 = new node(8);head->next = n2;n2->next = n3;n3->next = n4;n4->next = n5;n5->next = n6;n6->next = n7;n7->next = n8;cout<<findminnode(head)->d<<endl;cout<<endl;n8->next = n3;node * jiao ;bool an = ishascycle(head,jiao);cout<<an<<endl;node *jiaodian = findfirstnode(head);cout<<jiaodian->d<<endl;cout<<endl;n8->next = NULL;node *p = reve(head);while(p){cout<<p->d<<" ";p= p->next;}cout<<endl;}