Re: help on cartesianProduct()

[Era Scarecrow via Digitalmars-d-learn]

On Sunday, 11 December 2016 at 18:05:19 UTC, Era Scarecrow wrote:
On Sunday, 11 December 2016 at 16:34:38 UTC, Orut wrote:
I need to be able to vary the number of ranges to feed into 
cartesianProduct() at run time.

 Hmmm... what kind of ranges? Are they going to be arrays? Or 
something else?


Well, with the assumption of using arrays (since you kinda need a 
length for it to work) I've thrown together a quick struct that 
does the job. Not fully tested, but will do the same thing with a 
varying number of inputs.

[code]
struct MultiCart(T) {
    T[][] data;
    int iteration;
    int max;

    this(T[][] _d, int iter=0) {
        data = _d;
        iteration = iter;

        max = 1;
        foreach(a; _d) {
            if (a.length)
                max *= a.length;
        }
    }

    T[] front() {
        int i = iteration;
        T[] val;

        foreach(d; data) {
            if (d.length) {
                val ~= d[i % d.length];
                i /= d.length;
            }
        }

        return val;
    }

    void popFront() {
        iteration++;
    }

    bool empty() {
        return iteration >= max;
    }
}

unittest {
    import std.stdio;
    alias CartInt = MultiCart!int;

    int[] a=[1,2,3],b=[4,5],c=[6,7];
    foreach(x; CartInt([a,b,c]))
        writeln(x);

    foreach(x; CartInt([a,b]))
        writeln(x);
}
[/code]