队列

应用：广搜

总结：链表总的来说比较灵活，普通的顺序表有一头是固定的，因此对于队列这种两端都存在数据变化的情况，使用链表实现会比较自然，而使用顺序表实现则要用循环队列的方式来弥补普通顺序表的不足。

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

#define COLOR(a, b) "\033[" #b "m" a "\033[0m"
#define RED(a) COLOR(a, 31)
#define GREEN(a) COLOR(a, 32)

//结构定义：队列(顺序表)
typedef struct Queue {
    int *data;
    int head, tail, size, length;
} Queue;

//结构操作
Queue *init(int size);
void clear(Queue *que);
int expand(Queue *que);
int push(Queue *que, int val);
int front(Queue *que);
int empty(Queue *que);
int pop(Queue *que);
void output(Queue *que);

int main() {
    srand(time(0));
    #define MAX_N 20
    Queue *que = init(1);
    for (int i = 0; i < MAX_N; i++) {
        int op = rand() % 4;
        int val = rand() % 100;
        switch (op) {
            case 0:
            case 1:
            case 2: {
                printf("push %d to the Queue = %d\n", val, push(que, val));
            } break;
            case 3: {
                if (empty(que)) {
                    printf("pop from the Queue = 0\n");
                } else {
                    printf("pop %d from the Queue = ", front(que));
                    printf("%d\n", pop(que));
                }
            } break;
        }
        output(que), printf("\n");
    }
    #undef MAX_N
    clear(que);
    return 0;
}

//结构操作：初始化队列
Queue *init(int size) {
    Queue *que = (Queue *)malloc(sizeof(Queue));
    que->data = (int *)malloc(sizeof(int) * size);
    que->head = que->tail = que->length = 0;
    que->size = size;
    return que;
}

//结构操作：销毁队列
void clear(Queue *que) {
    if (que == NULL) return;
    free(que->data);
    free(que);
    return;
}

//结构操作：队列扩容
int expand(Queue *que) {
    int extra_size = que->size;
    int *temp;
    while (extra_size) {
        temp = (int *)malloc(sizeof(int) * (que->size + extra_size));
        if (temp != NULL) break;
        extra_size >>= 1;
    }
    if (temp == NULL) return 0;
    for (int i = 0; i < que->length; i++) {
        temp[i] = que->data[(que->head + i) % que->size];
    }
    free(que->data);
    que->data = temp;
    que->head = 0;
    que->tail = que->length;
    que->size += extra_size;
    return 1;
}

//结构操作：入队
int push(Queue *que, int val) {
    if (que == NULL) return 0;
    if (que->length == que->size) {
        if (!expand(que)) {
            printf(RED("fail to expand!\n"));
            return 0;
        }
        printf(GREEN("success to expand! the new size = %d\n"), que->size);
    }
    que->data[que->tail++] = val;
    if (que->tail == que->size) que->tail = 0;
    que->length += 1;
    return 1;
}

//结构操作：访问队首元素
int front(Queue *que) {
    return que->data[que->head];
}

//结构操作：队列判空
int empty(Queue *que) {
    return que->length == 0;
}

//结构操作：出队
int pop(Queue *que) {
    if (que == NULL) return 0;
    if (empty(que)) return 0;
    que->head += 1;
    if (que->head == que->size) que->head = 0;
    que->length -= 1;
    return 1;
}

//结构操作：输出所有元素
void output(Queue *que) {
    printf("Queue(%d): [", que->length);
    for (int i = 0; i < que->length; i++) {
        i && printf(", ");
        printf("%d", que->data[(que->head + i) % que->size]);
    }
    printf("]\n");
    return;
}

链队列

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

#define COLOR(a, b) "\033[" #b "m" a "\033[0m"
#define RED(a) COLOR(a, 31)
#define GREEN(a) COLOR(a, 32)

//结构定义：链表节点
typedef struct Node {
    int data;
    Node *next;
} Node;

//结构定义：队列(链表)
typedef struct Queue {
    Node head, *tail; // 定义虚拟头节点 (index = -1) for 入队时可以统一操作
    int length;
} Queue;

//结构操作
Node *getNewNode(int val);
Queue *init();
void clear_node(Node *node);
void clear(Queue *que);
int push(Queue *que, int val);
int front(Queue *que);
int empty(Queue *que);
int pop(Queue *que);
void output(Queue *que);

int main() {
    srand(time(0));
    #define MAX_N 20
    Queue *que = init();
    for (int i = 0; i < MAX_N; i++) {
        int op = rand() % 4;
        int val = rand() % 100;
        switch (op) {
            case 0:
            case 1:
            case 2: {
                printf("push %d to the Queue = %d\n", val, push(que, val));
            } break;
            case 3: {
                if (empty(que)) {
                    printf("pop from the Queue = 0\n");
                } else {
                    printf("pop %d from the Queue = ", front(que));
                    printf("%d\n", pop(que));
                }
            } break;
        }
        output(que), printf("\n");
    }
    #undef MAX_N
    clear(que);
    return 0;
}

//结构操作：获得一个新节点
Node *getNewNode(int val) {
    Node *node = (Node *)malloc(sizeof(Node));
    node->data = val;
    node->next = NULL;
    return node;
}

//结构操作：初始化队列
Queue *init() {
    Queue *que = (Queue *)malloc(sizeof(Queue));
    que->head.next = NULL;
    que->tail = &(que->head);
    que->length = 0;
    return que;
}

//结构操作：释放一个节点
void clear_node(Node *node) {
    if (node == NULL) return;
    free(node);
    return;
}

//结构操作：销毁队列
void clear(Queue *que) {
    if (que == NULL) return;
    Node *node = que->head.next, *post_node;
    while (node != NULL) {
        post_node = node->next;
        clear_node(node);
        node = post_node;
    }
    free(que);
    return;
}

//结构操作：入队
int push(Queue *que, int val) {
    if (que == NULL) return 0;
    Node *node = getNewNode(val);
    que->tail->next = node;
    que->tail = node;
    que->length += 1;
    return 1;
}

//结构操作：访问队首元素
int front(Queue *que) {
    return que->head.next->data;
}

//结构操作：队列判空
int empty(Queue *que) {
    return que->length == 0;
}

//结构操作：出队
int pop(Queue *que) {
    if (que == NULL) return 0;
    if (empty(que)) return 0;
    Node *node = que->head.next;
    que->head.next = node->next;
    clear_node(node);
    que->length -= 1;
    if (que->length == 0) que->tail = &(que->head);
    return 1;
}

//结构操作：输出所有元素
void output(Queue *que) {
    printf("Queue(%d): [", que->length);
    for (Node *node = que->head.next; node != NULL; node = node->next) {
        node != que->head.next && printf(", ");
        printf("%d", node->data);
    }
    printf("]\n");
    return;
}