friends list

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct plist plist;
typedef struct {
  char *name;
  plist *friends;
} person;
struct plist {
  person *data;
  plist *next;
};
static person *person_alloc(char *name) {
  person *new = calloc(sizeof(*new), 1);
  new->name = strdup(name), new->friends = NULL;
  return new;
}
static void print_person(person *p) {
  printf("Name: %s, friends: { ", p->name);
  for (plist *pl = p->friends; pl; pl = pl->next) {
    printf("%s, ", pl->data->name);
  }
  puts("}");
}
static void plist_add(plist **plp, person *p) {
  plist *new = calloc(sizeof(*new), 1);
  new->data = p, new->next = *plp, *plp = new;
}
static void become_friends(person *p1, person *p2) {
  plist_add(&(p1->friends), p2), plist_add(&(p2->friends), p1);
}
static void print_common_friends(person *p1, person *p2) {
  printf("%s and %s have common friends: { ", p1->name, p2->name);
  for (plist *pl1 = p1->friends; pl1; pl1 = pl1->next) {
    for (plist *pl2 = p2->friends; pl2; pl2 = pl2->next) {
      if (pl1->data == pl2->data) { printf("%s, ", pl1->data->name); }
    }
  }
  puts("}");
}
typedef struct pqueue_data pqueue_data;
struct pqueue_data {
  person *person;
  int hop;
  pqueue_data *next;
};
typedef struct pqueue pqueue;
struct pqueue {
  pqueue_data *head, *tail;
};
static void plist_free(plist *pl) {
  if (!pl) { return; }
  plist_free(pl->next), free(pl);
}
static void person_free(person *p) {
  if (!p) { return; }
  plist_free(p->friends), free(p->name), free(p);
}
static int plist_contains(plist *pl, person *p) {
  if (!pl) { return 0; }
  if (pl->data == p) { return 1; }
  return plist_contains(pl->next, p);
}
static pqueue *pqueue_alloc(void) {
  pqueue *new = calloc(sizeof(*new), 1);
  new->head = new->tail = NULL;
  return new;
}
static pqueue_data *pqueue_data_alloc(person *p, int hop) {
  pqueue_data *new = calloc(sizeof(*new), 1);
  new->person = p, new->hop = hop, new->next = NULL;
  return new;
}
static void pqueue_data_free(pqueue_data *p) {
  if (!p) { return; }
  pqueue_data_free(p->next), free(p);
}
static void pqueue_free(pqueue *q) {
  if (!q) { return; }
  pqueue_data_free(q->head), free(q);
}
static void pqueue_put(pqueue *q, person *p, int n) {
  pqueue_data *new = pqueue_data_alloc(p, n);
  if (!q->head) {
    q->head = q->tail = new;
    return;
  }
  q->tail->next = new, q->tail = new;
}
static int pqueue_get(pqueue *q, person **pp, int *np) {
  if (!q->head) { return 0; }
  *pp = q->head->person, *np = q->head->hop;
  if (q->head == q->tail) {
    pqueue_data_free(q->head), q->head = q->tail = NULL;
  } else {
    pqueue_data *p = q->head;
    q->head = p->next, p->next = NULL, pqueue_data_free(p);
  }
  return 1;
}
static int access_ok1(person *p1, person *p2, plist **visited, pqueue *q,
                      int maxhop) {
  person *p;
  int hop;
  pqueue_put(q, p1, 0);
  while (pqueue_get(q, &p, &hop)) {
    plist_add(visited, p);
    if (maxhop < hop) { return 0; }
    if (plist_contains(p2->friends, p)) { return 1; }
    for (plist *pl = p->friends; pl; pl = pl->next) {
      person *f = pl->data;
      if (!plist_contains(*visited, f)) { pqueue_put(q, f, hop + 1); }
    }
  }
  return 0;
}
static int access_ok(person *p1, person *p2, int maxhop) {
  plist *visited = NULL;
  pqueue *q = pqueue_alloc();
  int result = access_ok1(p1, p2, &visited, q, maxhop);
  pqueue_free(q), plist_free(visited);
  return result;
}
int main(void) {
  person *alice = person_alloc("Alice"), *bob = person_alloc("Bob"),
         *carol = person_alloc("Carol"), *dave = person_alloc("Dave"),
         *ellen = person_alloc("Ellen"), *frank = person_alloc("Frank");
  become_friends(alice, bob), become_friends(alice, carol),
      become_friends(bob, dave), become_friends(carol, dave),
      become_friends(carol, ellen), become_friends(carol, frank),
      become_friends(dave, ellen), become_friends(ellen, frank);
  person *person_array[] = {alice, bob, carol, dave, ellen, frank};
  size_t size = sizeof(person_array) / sizeof(person_array[0]);
  { print_person(alice), print_person(bob), print_person(frank); }
  { print_common_friends(alice, frank); }
  {
    int c = 0;
    for (size_t hop = 0; hop < size; ++hop, c = 0) {
      printf("!%zd hop friend\n", hop);
      for (size_t i = 0; i < size; ++i) {
        for (size_t j = 0; j < size; ++j) {
          if (i == j) { continue; }
          if (access_ok(person_array[i], person_array[j], hop)) {
            printf("  %s --> %s\n", person_array[i]->name,
                   person_array[j]->name);
            ++c;
          }
        }
      }
      if ((int)size * ((int)size - 1) <= c) { break; }
    }
  }
  {
    for (size_t i = 0; i < size; ++i) { person_free(person_array[i]); }
  }
}