/**
 * @file
 * @brief [Subset-sum](https://en.wikipedia.org/wiki/Subset_sum_problem) (only
 * continuous subsets) problem
 * @details We are given an array and a sum value. The algorithms find all
 * the subarrays of that array with sum equal to the given sum and return such
 * subarrays count. This approach will have \f$O(n)\f$ time complexity and
 * \f$O(n)\f$ space complexity. NOTE: In this problem, we are only referring to
 * the continuous subsets as subarrays everywhere. Subarrays can be created
 * using deletion operation at the end of the front of an array only. The parent
 * array is also counted in subarrays having 0 number of deletion operations.
 *
 * @author [Swastika Gupta](https://github.com/Swastyy)
 */

#include <cassert> /// for assert
#include <cstdint>
#include <iostream> /// for IO operations
#include <unordered_map> /// for unordered_map
#include <vector> /// for std::vector

/**
 * @namespace backtracking
 * @brief Backtracking algorithms
 */
namespace backtracking {
/**
 * @namespace subarray_sum
 * @brief Functions for the [Subset
 * sum](https://en.wikipedia.org/wiki/Subset_sum_problem) implementation
 */
namespace subarray_sum {
/**
 * @brief The main function that implements the count of the subarrays
 * @param sum is the required sum of any subarrays
 * @param in_arr is the input array
 * @returns count of the number of subsets with required 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

/**
 * @brief Self-test implementations
 * @returns void
 */
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;
}

/**
 * @brief Main function
 * @returns 0 on exit
 */
int main() {
 test(); // run self-test implementations
 return 0;
}