队列实现(链表)

链式结构

#include <stdio.h>
#include <stdlib.h>

typedef int ElemType;

typedef enum {underflow, success, fatal} Status;

typedef struct node{
  ElemType ele;
  struct node * next;
}Node,*NodePtr;

typedef struct queue{
  Node* head;
  Node* tail;
}Queue, *QueuePtr;

栈操作

1. 初始化 :

时间复杂度: O(1)

Status initQueue(QueuePtr *queue_ptr) {
  Status s = success;
  (*queue_ptr) = (QueuePtr) malloc(sizeof(Queue));
  if(!(*queue_ptr)){
    s = fatal;
    return s;
  }

  NodePtr tmp = (NodePtr) malloc(sizeof(Node));
  if(tmp) {
    tmp -> next = NULL;
    (*queue_ptr) -> head = tmp;
    (*queue_ptr) -> tail = tmp;
  } else{
    s = fatal;
  }
  return s;
}

2. 清空 :

时间复杂度: O(1)

void clearQueue(QueuePtr queue_ptr){
  queue_ptr ->head = NULL;
  queue_ptr ->tail = NULL;
}

3. 销毁 :

时间复杂度: O(1)

void destroyQueue(QueuePtr *queue_ptr){
  NodePtr freeNode = (*queue_ptr) -> head -> next;
  while(freeNode){
    (*queue_ptr) -> head = freeNode->next;
    free(freeNode);
    freeNode = (*queue_ptr)->head->next;
  }
  freeNode = NULL;
  free((*queue_ptr));
  (*queue_ptr) = NULL;
}

4. 入队列 :

时间复杂度: O(1)

Status pushQueue(QueuePtr queue_ptr, ElemType ele){
  Status s = success;
  NodePtr newNode = (NodePtr)malloc(sizeof(Node));
  if (newNode){
    newNode ->ele = ele;
    newNode ->next = NULL;
    queue_ptr ->tail ->next = newNode;
    queue_ptr ->tail = newNode;
  } else {
    s = fatal;
  }
  return s;
}

5. 出队列 :

时间复杂度: O(1)

Status popQueue(QueuePtr queue_ptr,ElemType *ele) {
  Status s = success;
  if(isEmpty(queue_ptr)){
    s = underflow;
  } else {
    Node *deleteNode = queue_ptr -> head -> next;
    *ele = deleteNode -> ele;
    queue_ptr -> head -> next = deleteNode -> next;
    free(deleteNode);
    deleteNode = NULL;
    if(queue_ptr->head->next == NULL){    //该队列只有一个元素
      queue_ptr -> tail = queue_ptr -> head;
    }
  }
  return s;
}

6. 判断队列空 :

时间复杂度: O(1)

bool isEmpty(QueuePtr queue_ptr){
  if(queue_ptr->head == queue_ptr -> tail) return true;
  return false;
}

7. 获取队列大小 :

时间复杂度: O(1)

int getLength(QueuePtr queue_ptr){
  if(!isEmpty(queue_ptr)) {
    int count = 0;
    NodePtr tmp = queue_ptr-> head ->next;
    while(tmp) {
      count ++;
      tmp = tmp->next;
    }
    return count;
  }
  return 0;
}

8. 打印队列 :

时间复杂度: O(1)

void printQueue(QueuePtr queue_ptr) {
  if(!isEmpty(queue_ptr)) {
    printf("head <- tail\n");

    NodePtr tmp = queue_ptr->head->next;
    while(tmp){
      printf("%d ", tmp->ele);
      tmp = tmp->next;
    }
    printf("\n");

  }
}

问题解决

• 不用提前分配队列长度.