隊列實現(循環隊列、鏈式隊列)

隊列(Queue)是一種類似棧的數據結構, 棧是"後進先出", 而隊列是"先進先出"; 隊列通常模擬進出一致的數據處理場景, 例如消息推送處理, 商城中的購物處理等.

循環隊列預備知識:

• 循環隊列無法區分隊空或隊滿, 解決辦法: rear+1 == front mod 數組長度
• 隊空條件: front==rear (初始值: front = rear)
• 判斷隊滿: (rear+1)%MAXQSIZE == front
• 隊列長度: (rear - front + MAXQSIZE) % MAXSIZE
• 最大存儲 MAX_SIZE - 1 個元素

鏈式隊列預備知識

• 一般使用帶頭鏈表實現, 初始化時front和rear指針指向此元素
• 判斷隊列是否爲空: front==rear
• 第一個隊列元素: front.next

循環隊列(數組)

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

#define ERROR 0
#define OK 1
#define TRUE 1
#define FALSE 0
#define OVERFLOW -1
#define MAX_SIZE 5


typedef int ElemType;
typedef int status;

typedef struct {
    ElemType *base;
    int front;
    int rear;
} SqQueue;

status InitQueue(SqQueue &Q) {
    if (!Q.base) exit(OVERFLOW);
    Q.base = (ElemType *) malloc(sizeof(ElemType) * MAX_SIZE);
    Q.rear = Q.front = 0;
    return OK;
}

status EnQueue(SqQueue &Q, ElemType e) {
    if (!Q.base) return ERROR;
    if ((Q.rear + 1) % MAX_SIZE == Q.front)exit(OVERFLOW);
    Q.base[Q.rear] = e;
    Q.rear = (Q.rear+1) % MAX_SIZE;
    return OK;
}


status DeQueue(SqQueue &Q, ElemType &e) {
    if (!Q.base) return ERROR;
    e = Q.base[Q.front];
    Q.front = (Q.front+1) % MAX_SIZE;
    return OK;
}

status isEmpty(SqQueue Q) {
    if(Q.rear == Q.front) return TRUE;
    return FALSE;
}

int main() {
    SqQueue Q;
    InitQueue(Q);
    EnQueue(Q,1);
    EnQueue(Q,2);
    EnQueue(Q,3);
    EnQueue(Q,4);

    ElemType e;
    DeQueue(Q,e);
    EnQueue(Q,5);
    while(!isEmpty(Q)){
        DeQueue(Q,e);
        printf("%d\n",e);
    }
    return 0;
}

鏈式隊列

typedef struct QNode {
    ElemType data;
    struct QNode *next;
} QNode, *QNodePtr;

typedef struct {
    QNodePtr front;
    QNodePtr rear;
} *LinkQueue;

void InitLinkQueue(LinkQueue &Q) {
    Q = (LinkQueue)malloc(sizeof(LinkQueue));
    QNode *node = new QNode;//頭結點
    node->data = -1;
    node->next = NULL;
    Q->front = node;
    Q->rear = node;
}

status EnLinkQueue(LinkQueue &Q, ElemType e) {
    if (!Q) exit(OVERFLOW);
    QNode *p = new QNode;
    p->data = e;
    p->next = NULL;

    Q->rear->next = p;
    Q->rear = p;
    return OK;
}

status DeLinkQueue(LinkQueue &Q, ElemType &e) {
    if (!Q)return ERROR;
    if (Q->rear == Q->front) return ERROR;

    QNodePtr de_node = Q->front->next;
    e = de_node->data;
    if (de_node == Q->rear) {
        Q->rear = Q->front;
    } else {
        Q->front->next = de_node->next;
    }
    free(de_node);
    return OK;
}

status DestroyLinkQueue(LinkQueue &Q){
    if(!Q)return ERROR;
    if(Q->front==Q->rear)return OK;//無內容
    QNodePtr p;
    while(Q->front != Q->rear){
        p = Q->front->next;
        Q->front->next = p->next;
        free(p);
    }
    Q->rear = Q->front;
    return OK;
}

status isEmpty(LinkQueue Q) {
    if (Q->front == Q->rear) return TRUE;
    return FALSE;
}

int length(LinkQueue Q){
    QNodePtr p = Q->front;
    int n=0;

    while(p != Q->rear){
        n++;
        p = p->next;
    }
    return n;
}

int main(){
    LinkQueue Q;
    InitLinkQueue(Q);
    EnLinkQueue(Q,1);
    EnLinkQueue(Q,2);
    EnLinkQueue(Q,3);
    EnLinkQueue(Q,4);

    printf("len: %d\n",length(Q));

    ElemType e;
    while(!isEmpty(Q)){
        DeLinkQueue(Q, e);
        printf("%d\n",e);
    }
    return 0;
}