Given a clock, rearrange six consecutive numbers on its face, so the sum of every pair of adjacent numbers is a prime.

In C. Same approach as Charlie generally - with same result. I ripped the exhaustive permutation algorithm off inet.

Would it be good to have black out times where people cant post for a while so it is not sooo first come first solve? But I guess that is part of flooble. The shark feeding frenzy.

result

clock 1 2 3 4 9 10 7 6 5 8 11 12
clock 1 2 3 4 7 10 9 8 5 6 11 12

prog

#include <stdio.h>

int level = -1;
int start = 0;

int notPrime(int sum) {
  int primes[10] = {1,2,3,5,7,11,13,17,19,23}, i;
  for(i = 0; i < 10; i++)
    if (sum == primes[i])
      return 0;
  return 1;
}

int clkPrime(int *v) {
  int clk[12] = {0,};
  int i, temp;
  /*
  printf("clkPrime() : %d %d %d %d %d %d start %d\n",
  v[0], v[1], v[2], v[3], v[4], v[5], start);
  */
  //init clk to normal clock
  for (i = 0; i < 12; i++)
    clk[i] = i + 1;

  //set renumbered six
  for (i = 0; i < 6; i ++) {
    temp = start + i;
    if (temp > 11)
      temp -= 12;
    clk[temp] = v[i] + start;
    if ( (clk[temp] > 11) )
      clk[temp] -= 12;
  }

  for ( i = 0; i < 11; i ++)
    if ( (notPrime(clk[i] + clk[i+1])) )
      return 0;
  if  (  (notPrime(clk[11] + clk[0])) )
    return 0;
  else
    return 1;
}

void print(const int *v)
{
  int i, s[12], j;
  for (i = 0; i < 12; i ++)
    s[i] = i + 1;

  j = start;
  for (i = 0; i < 6; i ++) {
    j = start + i;
    if (j > 11)
      j -= 12;
    s[j] = v[i] + start;
    if (s[j] > 12)
      s[j] -= 12;
  }

  printf("clock %d %d %d %d %d %d %d %d %d %d %d %d \n",
  s[0], s[1], s[2], s[3], s[4], s[5], s[6], s[7], s[8], s[9], s[10], s[11]);
     
}   

void visit(int *Value, int k)
{
  int i;
  level++;
  Value[k] = level;
  if ( (Value[k] == 6 ) ) {
    if ( (clkPrime(Value)) )
 print(Value);
  }
  else
    for (i = 0; i < 6; i++)
      if (!(Value[i]) )
        visit(Value, i);

  level--;
  Value[k] = 0;
}

main()
{
  int Value[6], i;

  for (start = 0; start < 12; start++) {
    for (i = 0; i < 6; i++)
      Value[i] = 0;
    visit(Value, 0);
  }
}

Posted by vectorboy on 2004-08-12 17:06:32