generate all possible combinations of array values in C - c

Question

I have an array of N values from 0 to k (0 <= k <= N), I need to generate all possible combinations of N values
void generate(int n, int k) {
int q = -1;
char res = '|';
int r;
int j;
for (j = 1; j <= n; j++) {
q = j / (k + 1);
r = j % (k + 1);
printf("%d %c", r, res);
}
}
int main() {
int n = 2;
int k = 2;
int i, nbr_comb;
nbr_comb = pow((k + 1), n); number of combinations
for (i = 0; i < nbr_comb; i++) {
generate(n, i);
printf("\n");
}
return (EXIT_SUCCESS);
}
for this test (N=2 K=2) I had those combinations
0 |0 |
1 |0 |
1 |2 |
1 |2 |
1 |2 |
1 |2 |
1 |2 |
1 |2 |
1 |2 |
you see that it begins to generate but it fixed at a point, I can't find why ! ?
Expected Examples:
for n=2 k=2 n=3 k=2
0 0 0 0 0
0 1 0 0 1
0 2 0 0 2
1 0 1 0 0
1 1 1 0 1
1 2 1 0 2
2 0 1 1 0
2 1 1 1 1
2 2 1 1 2
1 2 0
1 2 1
1 2 2
2 0 0
.....

Answer 1

This is how your loops unfurl at n=2, k=2:
for (i=0; i<nbr_comb; i++)
i=0: generate(2,0) --> j=1: 1 mod 1 = 0
j=2: 2 mod 1 = 0
i=1: generate(2,1) --> j=1: 1 mod 2 = 1
j=2: 2 mod 2 = 0
i=2: generate(2,2) --> j=1: 1 mod 3 = 1
j=2: 2 mod 3 = 2
i=3: generate(2,3) --> j=1: 1 mod 4 = 1
j=2: 2 mod 4 = 2
i=4: generate(2,4) --> j=1: 1 mod 5 = 1
j=2: 2 mod 5 = 2
i=5: generate(2,5) --> j=1: 1 mod 6 = 1
j=2: 2 mod 6 = 2
i=6: generate(2,6) --> j=1: 1 mod 7 = 1
j=2: 2 mod 7 = 2
i=7: generate(2,7) --> j=1: 1 mod 8 = 1
j=2: 2 mod 8 = 2
i=8: generate(2,8) --> j=1: 1 mod 9 = 1
j=2: 2 mod 9 = 2
As you can see, your j for-loop in generate() just keeps calling modulo on j, the result of which will always be j once argument k is greater than j.
What you need is a nested for-loop that will take the current combination (range [0..(k+1)^n]) and the current array index (range [0..n-1]) into consideration when it decides which value to print from the set of [0..k].
If you think of the output as rows and columns, then in the right-most column, the value should change on each row, iterating from 0..k. In next column, the value should change every (k+1)th row. In next column, the value should change every (k+1)^2 row.
For example, when n = 3 and k = 2, then for the first 9 rows, the right-most column should look like 0,1,2,0,1,2,0,1,2. The middle column should look like 0,0,0,1,1,1,2,2,2. The left-most column should look like 0,0,0,0,0,0,0,0,0.
Thus, you end up with something like this:
int n = 2;
int k = 2;
int row, col;
int cell;
int rdiv;
int nbr_comb = pow(k+1, n);
for (row=0; row < nbr_comb; row++)
{
for (col=n-1; col>=0; col--)
{
rdiv = pow(k+1, col);
cell = (row/rdiv) % (k+1);
printf("%d |", cell);
}
printf("\n");
}