Bitwise Combination

gistfile1.c

#include<stdio.h>

void print_binary(long x, int digit)
{
  for (int i = 1 << (digit - 1); i; printf("%d", !!(x & i)), i >>= 1);
  puts("");
}

long next(long x)
{
  long b = x & -x;
  long t = x + b;
  long c = x ^ t;
  long m = (c >> 2) / b;
  return t | m;
}

int main()
{
  long c = 0, n = 6, k = 3;
  for (c = (1 << k) - 1; c < (1 << n); c = next(c)) print_binary(c, n);
  return 0;
}

/*

Output:

000111
001011
001101
001110
010011
010101
010110
011001
011010
011100
100011
100101
100110
101001
101010
101100
110001
110010
110100
111000

Algorithm:
http://realtimecollisiondetection.net/blog/?p=78

*/