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www/unix102/queue.txt

100 lines
1.5 KiB

#include <stdio.h>
#include <stdlib.h>
struct list {
int head;
struct list *tail;
};
typedef struct list list;
typedef struct {
list *front;
list *back;
} queue;
void list_free(list *lst) {
list *p;
while (lst != NULL) {
p = lst;
lst = lst->tail;
free(p);
}
}
list * cons(int val, list *lst) {
list *new = malloc(sizeof(list));
if (new == NULL) abort();
new->head = val;
new->tail = lst;
return new;
}
void list_print(list *lst) {
list *p = lst;
while (p != NULL) {
printf("%d ", p->head);
p = p->tail;
}
}
queue * make_queue() {
queue *new = malloc(sizeof(queue));
if (new == NULL) abort();
new->front = NULL;
new->back = NULL;
return new;
}
void push(int val, queue *q) {
if (q->front == NULL) { // empty queue
q->front = cons(val, NULL);
q->back = q->front;
}
else {
list *new = cons(val, NULL);
(q->back)->tail = new;
q->back = new;
}
}
int pop(queue *q) {
int val = (q->front)->head;
list *newhead = (q->front)->tail;
(q->front)->tail = NULL;
list_free(q->front);
q->front = newhead;
return val;
}
void queue_print(queue *q) {
printf("back ");
list_print(q->front);
printf("front\n");
}
void queue_free(queue *q) {
list_free(q->front);
free(q);
}
int main() {
queue *q = make_queue();
push(5, q);
push(3, q);
push(1, q);
queue_print(q);
printf("popped %d!\n", pop(q));
queue_print(q);
queue_free(q);
return 0;
}