L15

var DNA_LENGTH = 500; // 每個火箭的基因長度
var SIZE = 30; // 每一個世代的火箭個數
var rockets = []; // 存放所有的火箭

// 初始化所有的火箭
for (var i = 0; i < SIZE; i++) {
    var rocket = new Rocket();
    rocket.gens = randomGens();
    rocket.fire();
    rockets.push(rocket);
}

forever(function () {
    if (key.up) rockets[0].vy -= 0.3;
    if (key.right) rockets[0].vx += 0.1;
    if (key.left) rockets[0].vx -= 0.1;
});

// 當所有的火箭都停止，執行nextGeneration 產生下一代火箭
forever(function() {
    for (var i = 0; i < rockets.length; i++) {
        if (rockets[i].active) return;
    }
    nextGeneration();
});

// 產生隨機的初始化基因
function randomGens () {
    var gens = [];
    for (var i = 0; i < DNA_LENGTH; i++) {
        var num = Math.floor(Math.random() * 4);
        gens.push(num);
    }
    return gens;
}

// 產生下一個世代
function nextGeneration () {

    for (var i = 0; i < SIZE; i++) {
        var rocket = rockets[i];
        var score1 = Math.abs(platform.x - rocket.x);
        var score2 = Math.abs(rocket.vy);
        rockets[i].score = score1 + score2;
    }

    rockets.sort(function(a, b) {
        return a.score - b.score;
    });

    bestGens = rockets[0].gens;
    subGens = rockets[1].gens;

    for (var i = 0; i < SIZE; i++) {
        rockets[i].gens = crossover(bestGens, subGens);
        rockets[i].fire();
    }
}

// 交配產生下一代基因
// 每個基因有 2% 的機率突變，若不突變則各有 50% 的機率來自父親和母親
function crossover (a, b) {
    var gens = [];
    for (var i=0; i<DNA_LENGTH; i++) {
        gens[i] = Math.random() > 0.5 ? a[i] : b[i];
        if (Math.random() < 0.02) gens[i] = Math.floor(Math.random()*4);
    }
    return gens;
}