TheAlgorithms-C-Plus-Plus/backtracking/subset_sum.cpp

/**
 * @file
 * @brief Program to Count number of subsets
 *
 * @details Subset problem (https://en.wikipedia.org/wiki/Subset_sum_problem)
 * @author [Swastika Gupta](https://github.com/swastyy)
 */

#include <cassert>   /// for assert
#include <iostream>  /// for io operations
#include <vector>    /// for std::vector

/**
 * @namespace backtracking
 * @brief subset sum algorithm
 */
namespace backtracking {
/**
 * @namespace Subsets
 * @brief Functions for counting subsets in a given array with a given sum
 * Time Complexity: O(n * 2^n), where ‘n’ is the number of elements in the given array.
 * size of the array.
 */
namespace Subsets {
/**
 * @brief The main function implements count of subsets
 * @param sum is the required sum of any subset
 * @param in_arr is the input array
 * @returns count of the number of subsets with required sum
 */

std::uint64_t subset_sum(int sum, const std::vector<int> &in_arr) {
    int nelement = in_arr.size();
    int count_of_subset = 0;

    for (int i = 0; i < (1 << (nelement)); i++) {
        int check = 0;
        for (int j = 0; j < nelement; j++) {
            if (i & (1 << j)) {
                check += (in_arr[j]);
            }
        }
        if (check == sum) {
            count_of_subset++;
        }
    }
    return count_of_subset;
}
}  // namespace Subsets
}  // namespace backtracking

/**
 * @brief Test implementations
 * @returns void
 */
static void test() {
    // Test 1
    std::cout << "1st test ";
    std::vector<int> array1 = {-7, -3, -2, 5, 8};  // input array
    assert(backtracking::Subsets::subset_sum(0, array1) ==
           2);  // first argument in subset_sum function is the required sum and
                // second is the input array
    std::cout << "passed" << std::endl;

    // Test 2
    std::cout << "2nd test ";
    std::vector<int> array2 = {1, 2, 3, 3};
    assert(backtracking::Subsets::subset_sum(6, array2) ==
           3);  // here we are expecting 3 subsets which sum up to 6 i.e.
                // {(1,2,3),(1,2,3),(3,3)}
    std::cout << "passed" << std::endl;

    // Test 3
    std::cout << "3rd test ";
    std::vector<int> array3 = {1, 1, 1, 1};
    assert(backtracking::Subsets::subset_sum(1, array3) ==
           4);  // here we are expecting 4 subsets which sum up to 1 i.e.
                // {(1),(1),(1),(1)}
    std::cout << "passed" << std::endl;

    // Test 4
    std::cout << "4th test ";
    std::vector<int> array4 = {3, 3, 3, 3};
    assert(backtracking::Subsets::subset_sum(6, array4) ==
           6);  // here we are expecting 6 subsets which sum up to 6 i.e.
                // {(3,3),(3,3),(3,3),(3,3)}
    std::cout << "passed" << std::endl;

    // Test 5
    std::cout << "5th test ";
    std::vector<int> array5 = {};
    assert(backtracking::Subsets::subset_sum(6, array5) ==
           0);  // here we are expecting 0 subsets which sum up to 6 i.e. we can
                // select anything from an empty array
    std::cout << "passed" << std::endl;
}

/**
 * @brief Main function
 * @returns 0 on exit
 */
int main() {
    test();  // execute the test
    return 0;
}