ACM 136 - Ugly Numbers

#include<stdio.h>
#define min(a, b)  (a <b ? a : b)
#define min_3(a, b, c) min(min(a, b), c)

int main()
{
   int num = 0, p2, p3, p5, n;
   long a[1501];
   a[1] = p2 = p3 = p5 = n = 1;
   while(1)
   {  
      a[++ n] = min_3(2 * a[p2], 3 * a[p3], 5 * a[p5]);
      if(a[n] == 2 * a[p2]) p2++;
      if(a[n] == 3 * a[p3]) p3++;
      if(a[n] == 5 * a[p5]) p5++;
      if(n == 1500) break;
   }
   printf("The 1500'th ugly number is %ld.\n", a[n]);
   return 0;
}

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