import std.stdio : writeln;
import std.algorithm.comparison: min, equal;
import std.algorithm.iteration: sum;
import core.time: MonoTime, Duration;


auto sum_subranges(T)(T input, uint range)
{
    import std.range : chunks;
    import std.algorithm : map;

    if (range != 0)
    {
        return input.chunks(range).map!(sum);
    }
    return typeof(return).init;
}

void main()
{
    import std.range : iota, array;
    auto v = iota(0,1000000).array;
    int sum;
    MonoTime beg = MonoTime.currTime;
    for (int i=0; i < 100; i++)
        sum += cast(int)sum_subranges(v,2).length;
    MonoTime end = MonoTime.currTime;
    writeln(end-beg);
    writeln(sum);
    
    assert(equal(sum_subranges([1,1,1], 2), [2, 1]));
    assert(equal(sum_subranges([1,1,1,2,3,3], 2), [2, 3, 6]));
    assert(equal(sum_subranges(cast(int[])[], 2), cast(int[])[]));
    assert(equal(sum_subranges([1], 2), [1]));
}