prefix_sum_array.cpp

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#include <cassert>   
#include <iostream>  
#include <vector>    

namespace range_queries {
namespace prefix_sum_array {
 
std::vector<int64_t> PSA(1, 0);

void build(std::vector<int64_t> original_array) {
    for (int i = 1; i <= static_cast<int>(original_array.size()); i++) {
        PSA.push_back(PSA[i - 1] + original_array[i]);
    }
}

int64_t query(int64_t beg, int64_t end) { return PSA[end] - PSA[beg - 1]; }
 
}  // namespace prefix_sum_array
}  // namespace range_queries

static void test() {
    std::vector<int64_t> values{0,  123, 0,  2,  -2, 5,
                                24, 0,   23, -1, -1};  // original array
 
    range_queries::prefix_sum_array::build(values);
    // queries are of the type: sum of the range [a, b] = psa[b] - psa[a-1]
 
    assert(range_queries::prefix_sum_array::query(1, 10) ==
           173);  // sum of the entire array
    assert(range_queries::prefix_sum_array::query(4, 6) ==
           27);  // the sum of the interval [4, 6]
    assert(range_queries::prefix_sum_array::query(5, 9) ==
           51);  // the sum of the interval [5, 9]
}

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