30 lines
833 B
C
30 lines
833 B
C
/* calculates all subsets of the string comb by assigning eatch letter a position in a binary number and counting up. */
|
|
#include <stdio.h>
|
|
#include <string.h>
|
|
|
|
// #define DEBUG
|
|
|
|
int main() {
|
|
char* comb = "ABCD";
|
|
int count = strlen(comb);
|
|
// that bitshifting is the same is squaring count
|
|
int permutations = (1 << count);
|
|
|
|
printf("string is %s\nthere are %d permutations", comb, permutations);
|
|
|
|
for (unsigned char i = 0; i < permutations; i++) {
|
|
for (unsigned char j = 0; j < 4; j++) {
|
|
// when j=0, will result in 0b0001, when j=1, 0b0010, j=2 0b0100.
|
|
unsigned char mask = 1 << j;
|
|
#ifdef DEBUG
|
|
printf(" j=%x mask=%x, postmask=%x, i=%x", j, mask, (i & mask), i);
|
|
#endif /* ifdef DEBUG */
|
|
if ((i & mask) != 0) {
|
|
printf(" %c", comb[j]);
|
|
}
|
|
}
|
|
printf("\n");
|
|
}
|
|
|
|
return 0;
|
|
}
|