Genetic II.js

/*
    Using genetic algorithim
    Given an array of integers, say [-2, 9, 2, -5, 1, -3, -10, 6]
    Find a sum of elements that is closest to 0
    
    This solution finds the best solution on 100 rounds.
    The best solution is the Gene with it's defect closest to 0,
    with the maximum number of elements included,
    found on the earliest round possible
*/

function rand (num) {
    if (!num) {
        num = 1;
    }
    return Math.floor(Math.random() * num);
}

var NUMBERS_ARRAY_SIZE = 10;
var NUMBERS = (function () {
    var arr = [];
    for (var i = 0; i < NUMBERS_ARRAY_SIZE; i++) {
        arr.push(rand(10) * [1, -1][rand(2)]);
    }
    
    return arr;
}());

var GENE_LENGTH = NUMBERS.length;
var POPULATION_LENGTH = 20;
var SELECT_CUT = 1 / 2;
var ROUNDS = 100;

function Gene (seq, currentRound) {
    this.seq = seq;
    
    if (this.seq == null) {
        this.seq = [];
        for (var i = 0; i < GENE_LENGTH; i++) {
           this.seq.push([1, 0][rand(2)]); 
        }
    }
    
    if (currentRound == null) {
        currentRound = 0;
    }
    
    var sum = 0;
    var totalIns = 0;
    for (var i = 0; i < GENE_LENGTH; i++) {
        if (this.seq[i]) {
            sum += NUMBERS[i];
            totalIns += 1;
        }
    }
    
    this.defect = sum;
    this.totalIns = totalIns;
    this.round = currentRound;
}

Gene.prototype.compareTo = function (otherGene) {
    if (Math.abs(this.defect) < Math.abs(otherGene.defect)) {
        return -1;
    }
    
    if (Math.abs(this.defect) > Math.abs(otherGene.defect)) {
        return 1;
    }
    
    if (Math.abs(this.defect) === Math.abs(otherGene.defect)) {
        if (this.totalIns > otherGene.totalIns) {
            return -1;
        }
        
        if (this.totalIns < otherGene.totalIns) {
            return 1;
        }
    }
    
    return 0;
};

Gene.prototype.reproduceWith = function (otherGene) {
    var halfLength = Math.floor(this.seq.length / 2);
    var firstHalf = this.seq.slice(0, halfLength);
    var lastHalf = otherGene.seq.slice(halfLength);
    return new Gene(firstHalf.concat(lastHalf), this.round + 1);
};

function Population () {
    this.members = [];
    this.bestGene = null;
}

Population.prototype.generate = function () {
    // random initial population
    for (var i = 0; i < POPULATION_LENGTH; i++) {
        var gene = new Gene();
        this.members.push(gene);
    }
};

Population.prototype.sort = function () {
    this.members.sort(function (a, b) {
        return a.compareTo(b);
    });
    
    if (this.bestGene == null) {
        this.bestGene = this.members[0];
        return;
    }
    
    if (this.members[0].compareTo(this.bestGene)) {
        this.bestGene = this.members[0];
    }
    
};

Population.prototype.select = function () {
    // select best genes
    var selected = [];
    for (var i = 0; i < POPULATION_LENGTH * SELECT_CUT; i++) {
        selected.push(this.members[i]);
    }
    this.members = selected;
};

Population.prototype.reproduce = function () {
    // get the best individual, reproduce it with the second best, third and so on
    // if it doesn't fill the initial population, do the same with the second, and so on
    var firstParentIdx = 0;
    var secondParentIdx = 1;
    var newMembers = [];
    
    for (var i = 0; i < POPULATION_LENGTH; i++) {
        newMembers.push(this.members[firstParentIdx].reproduceWith(
            this.members[secondParentIdx])
        );
        
        secondParentIdx++;
        
        if (secondParentIdx >= this.members.length) {
            firstParentIdx++;
            secondParentIdx = firstParentIdx + 1; 
        }
    }
    
    this.members = newMembers;
};

Population.prototype.live = function () {
    for (var i = 0; i < ROUNDS; i++) {
        pop.sort();
        pop.select();
        pop.reproduce();
    }
    
    console.log(this.bestGene);
};

console.log(NUMBERS);
var pop = new Population();
pop.generate();
pop.live();