无头结点单链表

typedef struct LNode {
 int data;
 LNode *next;
}LNode,*LList;  //LList（实质为LNode*）的无头结点表头

bool isEmptyLList(LList L) { //判断是否空表
 if (L)
  return false;
 else
  return true;
}
void showLList(LList L) { //遍历输出链表各结点值
 if (isEmptyLList(L)) {
  cout << "Empty!" << endl;
  return;
 }
 LNode* showNode = L;
 while (showNode) {
  cout << showNode->data << " ";
  showNode = showNode->next;
 }
 cout << endl;
 return;
}
LNode* getLListTail(LList L) { //获取表尾结点
 LNode *tailNode = L;
 while (tailNode&&tailNode->next) {
  tailNode = tailNode->next;
 }
 return tailNode;
}
int getLListLength(LList L){ //获取链表长度
 int i = 0;
 LNode* curNode = L;
 if (!curNode) {
  return i;
 }
 while (curNode&&curNode->next) {
  curNode = curNode->next;
  i++;
 }
 return i+1;
}
LNode* getLListLocate(LList L,int i) { //获取第i个结点
 int len = getLListLength(L);
 if (i > len || i < 1) {
  return NULL; //非法值
 }
 LNode* locNode = L;
 for (i; i>1; i--) {
  locNode = locNode->next;
 }
 // while (i-->1) { locNode = locNode->next; }另一种循环方式
 return locNode;
}
int searchLList(LList L,int e) { //搜寻存储数值为e的首个结点编号，未找到返回NULL
 int i=1;
 LNode *searchNode = L;
 while (searchNode) {
  if (searchNode->data == e) {
   return i;
  }
  searchNode = searchNode->next;
  i++;
 }
 return NULL;
}
int searchLList(LList L, LNode* node) { //搜寻结点n的编号，未找到返回NULL
 int i = 1;
 LNode *searchNode = L;
 while (searchNode) {
  if (searchNode == node) {
   return i;
  }
  searchNode = searchNode->next;
  i++;
 }
 return NULL;
}
void preAddLList(LList &L,int e) { //头插法增加一个结点
 LNode *addNode = new LNode;
 addNode->data = e;
 if (isEmptyLList(L)) {
  addNode->next = NULL;
  L = addNode;
  return;
 }
 addNode->next = L;
 L = addNode;
 return;
}
void preSetLList(LList &L) { //循环头插创建链表
 int i;
 while (cin >> i) {
  if (i == '#')break;
  preAddLList(L, (int)i);
 }
 return;
}
int preDelLList(LList &L) { //头删法减少一个结点
 int e;
 if (isEmptyLList(L)) {
  cout << "Error: empty delete!" << endl;
  return NULL;
 }
 LNode* delNode = L;  //待删结点
 LNode* headNode = L->next; //新的表头
 e = delNode->data;
 L = headNode;
 delete delNode;
 return e;
}
void tailAddLList(LList &L,int e) { //尾插增加一个结点
 LNode *addNode = new LNode;
 LNode *tailNode = getLListTail(L);
 addNode->data = e;
 addNode->next = NULL;
 if (isEmptyLList(L)) {
  L = addNode;
  return;
 }
 tailNode->next = addNode;
 return;
}
void tailSetLList(LList &L) { //循环尾插创建链表
 int i;
 while (cin>>i) {
  if (i == '#')break;
  tailAddLList(L,(int)i);
 }
 return;
}
int tailDelLList(LList &L) { //尾删减少一个结点
 int e;
 int len = getLListLength(L);
 if (len < 1) {
  cout << "Error: empty delete!" << endl;
  return NULL;
 }
 if (len == 1) {
  delete L;
  L = NULL;
  return NULL;
 }
 LNode* predelNode = getLListLocate(L, len - 1);  //表尾前驱（新的表尾）
 LNode* delNode = predelNode->next;     //待删表尾
 e = delNode->data;
 predelNode->next = NULL;
 delete delNode;
 return e;
}