C语言设计前中后队列实例代码

目录

• 队列基本概念
• 1，数组实现
•  2，链表实现
•  总结

队列基本概念

队列是最常见的概念，日常生活经常需要排队，仔细观察队列会发现，队列是一种逻辑结构，是一种特殊的线性表。特殊在：

只能在固定的两端操作线性表

只要满足上述条件，那么这种特殊的线性表就会呈现出一种“先进先出”的逻辑，这种逻辑就被称为队列。

由于约定了只能在线性表固定的两端进行操作，于是给队列这种特殊的线性表的插入删除，起个特殊的名称：

队头：可以删除节点的一端

队尾：可以插入节点的一端

入队：将节点插入到队尾之后，函数名通常为enQueue()

出队：将队头节点从队列中剔除，函数名通常为outQueue()

取队头：取得队头元素，但不出队，函数名通常为front()

本题就是手撸数据结构中基本的队列结构，常用的有两种，一种是用链表实现，一种是数组实现。本文将会给出两种实现方式

1，数组实现

typedef struct {
    int value[1000];
    int len;
} FrontMiddleBackQueue;

FrontMiddleBackQueue* frontMiddleBackQueueCreate() {
    FrontMiddleBackQueue *queue = (FrontMiddleBackQueue *)malloc(sizeof(FrontMiddleBackQueue));
    memset(queue,0,sizeof(FrontMiddleBackQueue));
    return queue;
}

void insert(FrontMiddleBackQueue* obj, int pos, int val)
{
    //在pos位置插入val，则pos(从0开始)位置后的数统一向后挪一个位置,队列长度加1
    int i = 0;
    for(i=obj->len; i>pos; i--)
    {
        obj->value[i] = obj->value[i-1];
    }
    obj->value[pos] = val;
    obj->len++;
}

int pop(FrontMiddleBackQueue* obj, int pos)
{
    //弹出pos位置的val,则pos(从0开始)位置后向前统一挪一个位置，队列长度减一
    if(obj->len == 0)
        return -1;
    int i = 0;
    int popval = obj->value[pos]; //先将pos位置的数保存下来，不然下面的移位操作就覆盖了pos位置的值
    for(i=pos; i<obj->len-1; i++)
    {
        obj->value[i] = obj->value[i+1];
    }
    obj->len--;
    return popval;
}

void frontMiddleBackQueuePushFront(FrontMiddleBackQueue* obj, int val) {
    insert(obj,0,val);
}

void frontMiddleBackQueuePushMiddle(FrontMiddleBackQueue* obj, int val) {
    insert(obj,obj->len/2,val);
}

void frontMiddleBackQueuePushBack(FrontMiddleBackQueue* obj, int val) {
    insert(obj,obj->len,val);
}

int frontMiddleBackQueuePopFront(FrontMiddleBackQueue* obj) {
    return pop(obj,0);
}

int frontMiddleBackQueuePopMiddle(FrontMiddleBackQueue* obj) {
    return pop(obj,(obj->len-1)/2);
}

int frontMiddleBackQueuePopBack(FrontMiddleBackQueue* obj) {
    return pop(obj, obj->len-1);
}

void frontMiddleBackQueueFree(FrontMiddleBackQueue* obj) {
    free(obj);
}

/**
 * Your FrontMiddleBackQueue struct will be instantiated and called as such:
 * FrontMiddleBackQueue* obj = frontMiddleBackQueueCreate();
 * frontMiddleBackQueuePushFront(obj, val);

 * frontMiddleBackQueuePushMiddle(obj, val);

 * frontMiddleBackQueuePushBack(obj, val);

 * int param_4 = frontMiddleBackQueuePopFront(obj);

 * int param_5 = frontMiddleBackQueuePopMiddle(obj);

 * int param_6 = frontMiddleBackQueuePopBack(obj);

 * frontMiddleBackQueueFree(obj);
*/

运行结果

 2，链表实现

1，设计链表结构，链表维持一个头节点和尾结点，头节点始终在最前面并且头结点的data存储整个队列的节点数，尾结点始终是最后一个节点

2，设计插入节点函数和删除节点函数，push和pop操作只需要根据不同场景传入不同的参数即可完成统一的操作

typedef struct tag_Node {
    int data;
    struct tag_Node* next, *prev;
}Node;

typedef struct {
    Node* front;
    Node* rear;
} FrontMiddleBackQueue;

FrontMiddleBackQueue* frontMiddleBackQueueCreate() {
    FrontMiddleBackQueue* que = (FrontMiddleBackQueue *)malloc(sizeof(FrontMiddleBackQueue));
    que->front = (Node *)malloc(sizeof(Node));
    que->rear = (Node *)malloc(sizeof(Node));
    que->front->data = 0;
    que->front->next = NULL;
    que->rear->data = 0;
    que->rear->next = NULL;
    que->front->next = que->rear;
    que->rear->prev = que->front;

    return que;
}

void AddNode(FrontMiddleBackQueue* obj, Node *cur, int val)
{
    Node* addNode = (Node *)malloc(sizeof(Node));
    addNode->data = val;
    addNode->prev = cur->prev;
    addNode->next = cur;

    cur->prev->next = addNode;
    cur->prev = addNode;

    obj->front->data++;
    return;
}

Node* GetMiddleNode(FrontMiddleBackQueue* obj, bool isAdd)
{
    Node* tmp = obj->front->next;

    int len = isAdd ? (obj->front->data / 2) : ((obj->front->data - 1) / 2);
    for (int i = 0; i < len; i++) {
        tmp = tmp->next;
    }
    return tmp;
}

void frontMiddleBackQueuePushFront(FrontMiddleBackQueue* obj, int val) {
    AddNode(obj, obj->front->next, val);
    return;
}

void frontMiddleBackQueuePushMiddle(FrontMiddleBackQueue* obj, int val) {
    AddNode(obj, GetMiddleNode(obj, true), val);
    return;
}

void frontMiddleBackQueuePushBack(FrontMiddleBackQueue* obj, int val) {
    AddNode(obj, obj->rear, val);
    return;
}

int RemoveNode(FrontMiddleBackQueue* obj, Node* cur)
{
    if (obj->front->data == 0) {
        return -1;
    }
    cur->next->prev = cur->prev;
    cur->prev->next = cur->next;

    obj->front->data--;
    int item = cur->data;
    free(cur);
    return item;
}

int frontMiddleBackQueuePopFront(FrontMiddleBackQueue* obj) {
    return RemoveNode(obj, obj->front->next);
}

int frontMiddleBackQueuePopMiddle(FrontMiddleBackQueue* obj) {
    return RemoveNode(obj, GetMiddleNode(obj, false));
}

int frontMiddleBackQueuePopBack(FrontMiddleBackQueue* obj) {
    return RemoveNode(obj, obj->rear->prev);
}

void frontMiddleBackQueueFree(FrontMiddleBackQueue* obj) {
    while (RemoveNode(obj, obj->front->next) != -1);
    free(obj->front);
    free(obj->rear);
    free(obj);
    return;
}

/**
 * Your FrontMiddleBackQueue struct will be instantiated and called as such:
 * FrontMiddleBackQueue* obj = frontMiddleBackQueueCreate();
 * frontMiddleBackQueuePushFront(obj, val);

 * frontMiddleBackQueuePushMiddle(obj, val);

 * frontMiddleBackQueuePushBack(obj, val);

 * int param_4 = frontMiddleBackQueuePopFront(obj);

 * int param_5 = frontMiddleBackQueuePopMiddle(obj);

 * int param_6 = frontMiddleBackQueuePopBack(obj);

 * frontMiddleBackQueueFree(obj);
*/

运行结果：

 总结

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