Thursday, May 22, 2014

Problem 86 - Squirrel (and done with finals)

I finished my last final earlier this evening, so I will be free for a while to possibly solve Project Euler problems. I may find other things to pass my time, but nonetheless I expect I will get a good number done in the next couple of weeks. Anyway, as promised in my last post, I freed up Squirrel, so I used Squirrel on problem 86. Squirrel really is an easy language to script in. It's basically like python with curly braces. No wonder I keep coming back to it. Now that I am climbing in numbers, the code I write is starting to follow less and less directly from the problem. As the goal of this blog is to share my experiences using a bunch of programming languages, using Project Euler as the medium of the challenge, not to talk about Project Euler problems, I will not go into too much depth about why the code below produces a correct solution, though the reader can feel free to investigate themselves or read about it elsewhere. I will give a short summary of what's going on though. The problem asks about shortest paths on cuboids, but these shortest paths are along the hypotenuse of a right triangle if you unfold the cuboid. Anyway, with this, Squirrel is now my fourth most used language (behind only Python and J, which each have 5 problems solved, Squirrel is up to 4), and here is my solution, which runs in about 9.7s on my machine:
local cuboids = [];

for (local i = 0; i < 2000; ++i) {
    cuboids.append(0);
}

function gcd(a, b) {
    if (b == 0) {
        return a;
    } else {
        return gcd(b, a%b);
    }
}

function coprime(a, b) {
    return gcd(a,b) == 1;
}

function EuclidLeg1(m, n) {
    return square(m) - square(n);
}

function EuclidLeg2(m, n) {
    return 2*m*n;
}

function odd(x) {
    return x % 2 == 1;
}

function square(x) {
    return x * x;
}
function min(x, y) {
    if (x < y) {
        return x;
    } else {
        return y;
    }
}

function max(x, y) {
    return -min(-x, -y);
}

function countCuboids(l1k, l2k) {
    local pydiag = square(l1k) + square(l2k);
    if (l1k < 2000) {
        for (local i = (l2k/2); i > 0; --i) {
            if (l2k-i >= 2000) {
                return;
            } else {
                local d1 = square(l2k-i+l1k) + square(i);
                local d2 = square(l1k+i) + square(l2k-i);
                if (pydiag <= min(d1, d2)) {
                    cuboids[max(l2k-i, l1k)] += 1;
                }
            }
        }
    }
}

for (local m = 1; m < 60; ++m) {
    for (local n = 1; n < m; ++n) {
        if (odd(m-n) && coprime(m, n)) {
            local leg1 = EuclidLeg1(m, n);
            local leg2 = EuclidLeg2(m, n);
            for (local k=1; k * min(leg1, leg2) < 2000; ++k) {
                countCuboids(leg1 * k, leg2 * k);
                countCuboids(leg2 * k, leg1 * k);
            }
        }
    }
}

local count = 0;
for (local i = 0; i < 2000; ++i) {
    count += cuboids[i];
    if (count > 1000000) {
        print(i + "\n");
        break
    }
}


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