(use srfi-69)

(define VERTICES 25000)
(define EDGES 1000)

(define g (make-hash-table))

(define (insert-edges)
  (display "\n Hash-tables - Inserting edges\n")
  (do ((i 0 (+ i 1))) ((= i VERTICES))
    (do ((j 0 (+ j 1))) ((= j EDGES))
      (hash-table-set! g
                       i
                       `((,j))))))

(insert-edges)

$ csc -O3 list-in-hash-table.scm -o list-in-hash-table
$ time ./list-in-hash-table 

 Hash-tables - Inserting edges

real	0m8.961s
user	0m8.897s
sys	0m0.028s

---------------------------------------------------------------------------

// adjacency list implementation of graph using linked list in c - got from the web
#include <stdio.h>
#include <stdlib.h>

struct adj_node {
  int index;
  struct adj_node * next;
};

void make_adj(struct adj_node *nod, int adj) {
  struct adj_node *new_adj = (struct adj_node *)malloc(sizeof(struct adj_node));
  new_adj->index = adj;
  new_adj->next = NULL;

  while(nod->next != NULL) 
    nod = nod->next;

  nod->next = new_adj;
}

int main() {
  const int VERTEXES = 25000;
  const int EDGES = 1000;

  int i, j;
  struct adj_node graph[VERTEXES];

  printf(" C Graph library - Inserting edges");

  for(i = 0; i < VERTEXES; i++) {
    graph[i].index = i;
    graph[i].next = NULL;
   
    for (j = 1; j < EDGES; j++) {
      make_adj(&graph[i], j);
    }

  }

  return 0;
}

$ gcc -O3 c-graph.c -o c-graph
$ time ./c-graph 

 C Graph library - Inserting edges
real	0m27.340s
user	0m27.014s
sys	0m0.280s