subarray_sum.cpp

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#include <cassert>        
#include <cstdint>
#include <iostream>       
#include <unordered_map>  
#include <vector>         

namespace backtracking {
namespace subarray_sum {
uint64_t subarray_sum(int64_t sum, const std::vector<int64_t> &in_arr) {
    int64_t nelement = in_arr.size();
    int64_t count_of_subset = 0;
    int64_t current_sum = 0;
    std::unordered_map<int64_t, int64_t>
        sumarray;  // to store the subarrays count
                   // frequency having some sum value
 
    for (int64_t i = 0; i < nelement; i++) {
        current_sum += in_arr[i];
 
        if (current_sum == sum) {
            count_of_subset++;
        }
        // If in case current_sum is greater than the required sum
        if (sumarray.find(current_sum - sum) != sumarray.end()) {
            count_of_subset += (sumarray[current_sum - sum]);
        }
        sumarray[current_sum]++;
    }
    return count_of_subset;
}
}  // namespace subarray_sum
}  // namespace backtracking

static void test() {
    // 1st test
    std::cout << "1st test ";
    std::vector<int64_t> array1 = {-7, -3, -2, 5, 8};  // input array
    assert(
        backtracking::subarray_sum::subarray_sum(0, array1) ==
        1);  // first argument in subarray_sum function is the required sum and
             // second is the input array, answer is the subarray {(-3,-2,5)}
    std::cout << "passed" << std::endl;
 
    // 2nd test
    std::cout << "2nd test ";
    std::vector<int64_t> array2 = {1, 2, 3, 3};
    assert(backtracking::subarray_sum::subarray_sum(6, array2) ==
           2);  // here we are expecting 2 subsets which sum up to 6 i.e.
                // {(1,2,3),(3,3)}
    std::cout << "passed" << std::endl;
 
    // 3rd test
    std::cout << "3rd test ";
    std::vector<int64_t> array3 = {1, 1, 1, 1};
    assert(backtracking::subarray_sum::subarray_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;
 
    // 4rd test
    std::cout << "4th test ";
    std::vector<int64_t> array4 = {3, 3, 3, 3};
    assert(backtracking::subarray_sum::subarray_sum(6, array4) ==
           3);  // here we are expecting 3 subsets which sum up to 6 i.e.
                // {(3,3),(3,3),(3,3)}
    std::cout << "passed" << std::endl;
 
    // 5th test
    std::cout << "5th test ";
    std::vector<int64_t> array5 = {};
    assert(backtracking::subarray_sum::subarray_sum(6, array5) ==
           0);  // here we are expecting 0 subsets which sum up to 6 i.e. we
                // cannot select anything from an empty array
    std::cout << "passed" << std::endl;
}

int main() {
    test();  // run self-test implementations
    return 0;
}