/*
 * This code is from "Algorithms in C, Third Edition,"
 * by Robert Sedgewick, Addison Wesley Longman, 1998.
 */
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include "Point.h"
typedef struct node* link;
struct node { point p;  link next; };
link **grid; int G; float d; int cnt = 0;
gridinsert(float x, float y)
  { int i, j; link s;
    int X = x*G +1; int Y = y*G+1;
    link t = malloc(sizeof *t);
    t->p.x = x; t->p.y = y; 
    for (i = X-1; i <= X+1; i++)
      for (j = Y-1; j <= Y+1; j++)
        for (s = grid[i][j]; s != NULL; s = s->next)
          if (distance(s->p, t->p) < d) cnt++; 
    t->next = grid[X][Y]; grid[X][Y] = t;
  }
main(int argc, char *argv[])
 { int i, j, N = atoi(argv[1]);
   d = atof(argv[2]); G = 1/d;
   grid = malloc2d(G+2, G+2);
   for (i = 0; i < G+2; i++)
     for (j = 0; j < G+2; j++)
       grid[i][j] = NULL;
   for (i = 0; i < N; i++)
     gridinsert(randFloat(), randFloat());
   printf("%d edges shorter than %f\n", cnt, d);
 }