Raindrops demo code.

raindrops.d

import std.algorithm;
void main(string[] args)
{
    import std.stdio;
    // args[0] is the program name, args[1] through args[n] are the input strings.
    
    // first validate the input
    auto input = args[1 .. $];
    foreach(i; 1 .. input.length)
    {
        assert(input[i].length == input[i-1].length); // all same length
    }

    assert(input[0].length <= input.length); // can get to the house!

    int spaces = cast(int)input[0].length + 1; // add one space for the house (no raindrops can fall there)
    int ticks = cast(int)input.length + 1; // One tick extra for the starting state before you left your car.

    int[][] raindrops = new int[][](ticks, spaces);

    // beginning state, can only be starting at the car. We use int.max / 2 because
    // we are looking for the minimum, and int.max / 2 will always be the highest
    // thing. We divide by 2 to avoid integer overflow.
    raindrops[0][] = int.max / 2;
    raindrops[0][0] = 0; // start completely dry at the car

    int curtick = 0;
    foreach(droplist; input)
    {
        ++curtick;
        int hasDrop(int i)
        {
            if(i >= droplist.length)
                // in house
                return 0;
            if(droplist[i] == '1')
                return 1;
            return 0;
        }

        // handle first and last spaces specially
        raindrops[curtick][0] = min(raindrops[curtick - 1][0], raindrops[curtick - 1][1]) + hasDrop(0);
        raindrops[curtick][spaces - 1] = min(raindrops[curtick - 1][spaces - 1],
                                    raindrops[curtick - 1][spaces - 2]); // no raindrops in the house
        foreach(j; 1 .. spaces - 1)
        {
            raindrops[curtick][j] =
                min(raindrops[curtick - 1][j - 1], // move ahead one space
                    raindrops[curtick - 1][j],     // stand still
                    raindrops[curtick - 1][j + 1]) // move back one space
                + hasDrop(j); // add the new raindrop at this space
        }
    }

    // writeln(raindrops);
    // result is in the house
    writeln(raindrops[curtick][spaces - 1], " min raindrops");
}