To count number of quadruplets with sum = 0

[bearophileHUGS at lycos.com]

Mark Dufour:
> FWIW, the original program can also be compiled with Shed Skin (http://
> mark.dufour.googlepages.com), an experimental (static-)Python-to-C++
> compiler, resulting in a speedup of about 8 times for a single test
> with 500 tuples.

If we want to play, then this is a literal translation to D (I am not
much good in D yet, so maybe there are ways to improve this code a
bit), as you can see D syntax isn't that bad (I think sometimes D
copies some Python syntax):


// Compile with:   dmd -O -release solver.d
import std.stdio, std.stream, std.string;

void main() {
    size_t sch;
    size_t[size_t] h;
    size_t[] q,w,e,r;

    int nrow = -1;
    auto datafile = new File("m4000.txt", FileMode.In);
    foreach(char[] row; datafile) {
        if (nrow == -1) {
            q.length = row.atoi();
            w.length = row.atoi();
            e.length = row.atoi();
            r.length = row.atoi();
        } else {
            char[][] srow = row.split();
            q[nrow] = srow[0].atoi();
            w[nrow] = srow[1].atoi();
            e[nrow] = srow[2].atoi();
            r[nrow] = srow[3].atoi();
        }
        nrow++;
    }

    foreach (x; q)
        foreach (y; w)
            h[x+y]++;

    foreach (x; e)
        foreach (y; r) {
            size_t* pointer = -x-y in h;
            if (pointer)
                sch += *pointer;
            // simpler but slower:
            // if (-x-y in h)
            //     sch += h[-x-y];
    }

    writefln(sch);
}


On my PC with the 1000 lines file this is about 2.2 times faster than
my  Psyco version and about 4.6 times faster than the same code
without Psyco.

Bye,
bearophile