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

#define MAXSIZE 1000000

int computeLen ( int n, int len[] )
{
   int t, j;

   t = 0; j = n;
   while (len[n] == -1) {
      ++t;
      if (n % 2 == 0) n /= 2; else n = 3*n + 1;
      if (n >= MAXSIZE) {
         fprintf(stderr, "Array limit exceeded... n = %d\n", n);
         exit(1);
      }
   }
   t += len[n]; n = j; j = t;
   while (len[n] == -1) {
      len[n] = t;
      t--;
      if (n % 2 == 0) n /= 2; else n = 3*n + 1;
   }
   return j;
}

int main ()
{
   int n, B, len[MAXSIZE], t, max;

   printf("Enter bound: "); scanf("%d", &B);
   len[0] = len[1] = 0;
   for (n=2; n<MAXSIZE; ++n) len[n] = -1;
   printf("len[  1] =   0\n"); max = 0;
   for (n=1; n<=B; ++n) {
      t = computeLen(n,len);
      if (t > max) {
         printf("len[%3d] = %3d\n", n, t);
         max = t;
      }
   }
   exit(0);
}

Enter bound: 1000
len[  1] =   0
len[  2] =   1
len[  3] =   7
len[  6] =   8
len[  7] =  16
len[  9] =  19
len[ 18] =  20
len[ 25] =  23
len[ 27] = 111
len[ 54] = 112
len[ 73] = 115
len[ 97] = 118
len[129] = 121
len[171] = 124
len[231] = 127
len[313] = 130
len[327] = 143
len[649] = 144
len[703] = 170
len[871] = 178