循环链表（头指针）

//循环链表的使用(头指针)
#include <stdio.h>
#include <stdlib.h>

#define OK 1
#define TRUE 1
#define ERROR 0
#define FALSE 0

typedef struct elem {
  int n;
}elem;//可取合适的元素

typedef struct splist {
  elem data;
  splist* nest;
}splist,*list;//链表

//建立并初始化链表
int InitList(list &L) {
  L =(list) malloc(sizeof(splist));
  L->nest = L;
  L->data.n = 0;  //把每个元素都赋0
  return OK;
}

//建立链表并添加元素
int CreateList(list &L) {
  InitList(L);
  printf("请输入你要输入元素的个数：");
  list p,ps=L;//p用来为新结点开辟新的空间,ps指向L的最后一个的地址
  int n = 0;
  scanf("%d", &n);//存要放入结点的个数
  for (int j = 0; j < n; j++) {
    int m = 0;
    scanf("%d", &m);
    p = (list)malloc(sizeof(splist));
    p->data.n = m;
    p->nest = ps->nest;
    ps->nest = p;
    ps = p;
  }
  return OK;
}

//加入一个元素
int AddList(list &L,int i,int n) {  //i为要插入的位置，n为要插入的元素
  list p, k = L;
  if (i <= 0) return ERROR;
  for (int j = 1; j <=i - 1; j++) {
    k = k->nest;
    if (k == L) return ERROR;//判断有没有到最后一个
  }
  p = (list)malloc(sizeof(splist));//开辟新结点
  p->data.n = n;
  p->nest = k->nest;
  k->nest = p;
  return OK;
}

//删除结点
int DeleteList(list &L, int i) {
  if (i <= 0) return ERROR;
  list ps, k = L;//ps用来存放第i结点的地址，k用来存放第i-1个结点的地址
  for (int j = 1; j <= i - 1; j++) {
    k = k->nest;
    if (k->nest == L) return ERROR;
  }
  ps = k->nest;
  k->nest = k->nest->nest;
  free(ps);
  return OK;
}

//求出链表的长度,返回元素个数
int LengthList(list &L) {
  int length = 0;
  list k = L->nest;
  while (k != L) {
    length++;
    k = k->nest;
  }
  return length;
}

//判断链表是否为空
int EmptyList(list &L) {
  if (L->nest == L)  return TRUE;
  return FALSE;
}
//将链表的第i个结点的元素存到e中
int SearchList(list &L, int i, elem* e) {
  if (i <= 0) return ERROR;
  list k = L;
  for (int j = 1; j <= i ; j++) {
    k = k->nest;
    if (k == L) return ERROR;
  }
  e->n = k->data.n;
  return OK;
}

//清空链表
int ClearList(list &L) {
  list ps,k=L->nest;
  while (k != L) {
    ps = k;
    L->nest = k->nest;
    k = k->nest;
    free(ps);
  }
  return OK;
}

//销毁链表
int DestoryList(list &L) {
  list ps, k = L->nest;
  while (k != L) {
    ps = k;
    L->nest = k->nest;
    k = k->nest;
    free(ps);
  }
  free(L);
  return OK;
}

//将b链表连接在a的后面,直接在a上做改变
int ContactList(list &a, list &b) {
  if (EmptyList(b)) return ERROR;
  list ps_a=a->nest, ps_b=b->nest;
  while (ps_a->nest != a) {
    ps_a = ps_a->nest;
  }
  while (ps_b->nest != b) {
    ps_b = ps_b->nest;
  }
  ps_a->nest = b->nest;
  ps_b->nest = a;
  free(b);
  return OK;
}


int main()
{
  //list a,b;
  //CreateList(a);
  //CreateList(b);
  //ContactList(a, b);
  //int j = EmptyList(L);
  //DestoryList(L);
  //ClearList(L);
  //AddList(L, 6, 6);
  //DeleteList(L, 7);
  //int l = LengthList(L);
  //elem n;
  //elem* e = &n;
  //SearchList(L, 6, e);
  return 0;
}