C > Data Structures

Linked list queue example

Linked list queue example

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

struct qnode {
 int data;
 int prio;
 struct qnode *next;
};

void quein(struct qnode **, struct qnode **, int , int);
int quedel(struct qnode **, struct qnode **, int *, int *);

int main(void) {
 int tab[10] = {2, 8, 3, 5, 4, 9, 6, 7, 1, 0};
 struct qnode *first = NULL;
 struct qnode *last = NULL;
 int val, prio, i;

 for(i = 0; i < 10; i++) {
  val = tab[i], prio = i;
  printf("Inserting: value: %d with priority: %d\n", prio, val);
  quein(&first, &last, val, prio);
 }

 printf("=-=\n");

 for(i = 0; i < 11; i++) {
  val = tab[i], prio = i;
  if(quedel(&first, &last, &val, &prio) != -1)
   printf("Deleting: value: %d with priority: %d\n", prio, val);
 }

 return 0;
}

int quedel(struct qnode **first, struct qnode **last, int *prio, int *val) {
 struct qnode *tmp = NULL;

 if((NULL == *last) && (*last == *first)) {
  fprintf(stderr, "Empty queue.....\n");
  return -1;
 }

 *val = (*first)->data, *prio = (*first)->prio;
 tmp = *first, *first = (*first)->next;

 if(*last == tmp)
  *last = (*last)->next;
 free(tmp);

 return 0;
}

void quein(struct qnode **first, struct qnode **last, int prio, int val) {
 struct qnode *tmp  = NULL; 
 struct qnode *tmp1 = NULL;

 tmp = malloc(sizeof(struct qnode));

 tmp->data = val;
 tmp->prio = prio;
 tmp->next = NULL;

 if(*last == NULL) {
  *last = tmp;
  *first = *last;
  } else {
   if((*first)->prio < prio) {
    tmp->next = *first;
    *first = tmp;
   } else {
    if((*last)->prio > prio) {
     (*last)->next = tmp;
     *last = tmp;
    } else {
     tmp1 = *first;
     while((tmp1->next)->prio >= prio) {
      tmp1 = tmp1->next;
     }
     tmp->next = tmp1->next;
     tmp1->next = tmp;
    }
   }
  }

 return;
}