How Can I Efficiently Generate Combinations in C ?

Generating Combinations Efficiently in C

Determining combinations in C can be a challenging task, especially if you're looking for a flexible solution that handles varying input values.

A thoughtful approach to this problem involves employing the next_permutation function from the standard C library. This function generates all permutations of a vector incrementally. Here's how you can utilize this function:

#include <iostream>
#include <algorithm>
#include <vector>

int main() {
    int n, r;
    std::cin >> n;
    std::cin >> r;

    std::vector<bool> v(n);
    std::fill(v.end() - r, v.end(), true);

    do {
        for (int i = 0; i < n; ++i) {
            if (v[i]) {
                std::cout << (i + 1) << " ";
            }
        }
        std::cout << "\n";
    } while (std::next_permutation(v.begin(), v.end()));
    return 0;
}

This approach effectively creates a selection array (v) with r selector values. Subsequently, it iterates through all permutations of this selection array, printing the corresponding set members for selected positions.

For instance, if you provide the input "5 2" (S = {1, 2, 3, 4, 5} and r = 2), this algorithm will output:

1 2
1 3
1 4
1 5
2 3
2 4
2 5
3 4
3 5
4 5

This method provides an efficient and generalized solution for generating combinations in C .

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