题解 | #【模板】队列#

#include <stdio.h>
#include <stdlib.h>
#include<stdbool.h>
#include <string.h>
typedef struct Node*  PtrToNode ;
//链表节点
struct Node {
    int Data;
    PtrToNode Next;//指针
};
//队列
typedef PtrToNode Position ;
typedef struct QNode* Queue ;
struct QNode {
    Position front, rear;//头和尾指针
    int MaxSize;//最大容量
};
Queue CreatQueue() {
    //分配内存空间
    Queue Q = (Queue) malloc(sizeof(struct QNode));
    Q->front = NULL;
    Q->rear = NULL;
    Q->MaxSize =  100000;
    return Q;
}
//判断队列是否为空
bool IsEmpty(Queue Q) {
    return Q->front == NULL;
}
//插入操作,插入队尾
void push(Queue Q, int x) {
    Position NewCode = (Position) malloc(sizeof(struct Node));
    NewCode->Data = x;
    //插入尾部
    NewCode->Next = NULL;
    if (IsEmpty(Q)) {
        Q->front = Q->rear = NewCode;
    } else {
        Q->rear->Next = NewCode;
        Q->rear = NewCode;
    }
}
//删除操作,删除头部元素
int pop(Queue Q) {

    if (IsEmpty(Q)) {
        printf("error\n");
        return -1;
    }
    int x = Q->front->Data;
    Position temp = Q->front;
    Q->front = Q->front->Next;
    //当只有一个元素时
    if (Q->front == NULL) {
        Q->rear = NULL;
    }
    free (temp);//释放空间

    return x;
}
//输出队首，队首不出队
int Front(Queue Q) {
    if (IsEmpty(Q)) {
        printf("error\n");
        return -1; // 或者返回一个错误码
    }
    return  Q->front->Data;
}

int main() {
    //接收数字
    int num;
    scanf("%d", &num);
    //队列
    Queue Q = CreatQueue();
    //遍历
    for (int i = 0; i < num; i++) {
        char op[1000000];
        scanf("%s", op);
        if (strcmp(op, "push") == 0) {
            int x;
            scanf("%d", &x);
            push(Q, x);
        } else if (strcmp(op, "pop") == 0) {
            if (!IsEmpty(Q)) {
                printf("%d\n", pop(Q));
            } else {
                printf("error\n");
            }
        } else if (strcmp(op, "front") == 0) {
            if (!IsEmpty(Q)) {
                printf("%d\n", Front(Q));
            } else {
                printf("error\n");
            }
        }
    }
    return 0;
}