​

const popSize = 20;

let population = [];

const fitnesses = [];

​

let maxScore = 0;

let fittest = "";

​

function setup() {

  createCanvas(400, 400);

  // frameRate(1);

  // noLoop();

  for(let i = 0; i < popSize; i ++) {

    population.push(new DNA(goal.length, 0.3, 0.2));

    fitnesses.push(0);

  }

  print(fitness(goal, null))

}

​

function draw() {

  background(220);

  text(goal, width/4, height/4);

  text(fittest, width/4, height/3);

  text(maxScore, width/4, height/2);

  for(let i = 0; i < popSize; i ++) {

    text(pheno(population[i]), width/2, (height/popSize) * (i + 0.5));

  }

  nextGen();

}

​

function nextGen() {

  let total = 0;

  for(let i = 0; i < popSize; i ++) {

    const f = fitness(goal, population[i]);

    fitnesses[i] = f;

    total += f;

    if(f > maxScore) {

      maxScore = f;

      fittest = pheno(population[i]);

    }

  }

  let nextGen = [];

  for(let i = 0; i < popSize; i ++) {

    let a = randomPop(population, fitnesses, total);

    let b = randomPop(population, fitnesses, total);

    nextGen.push(a.breed(b));

  }

  population = nextGen;

}

​

function randomPop(p, f, totalFitness) {

  let s = random(totalFitness);

  let t = 0;

  for(let i = 0; i < f.length; i ++) {

    t += f[i];

    if(t > s) {

      return p[i];

    }

  }

}

​

function pheno(dna) {

  let s = "";

  if(!dna) {

    return "";

  }

  for(let i = 0; i < dna.length; i ++) {

    const n = (dna.dna[i] * 26) | 0;

    s += char(97 + n)

  }

  return s;

}

​

function fitness(goal, dna) {

  let p = pheno(dna);

  let score = 0;

  for(let i = 0; i < p.length; i ++) {

    let n1 = unchar(p[i]);

    let n2 = unchar(goal[i]);

    let s = abs(n1 - n2);

    if(s === 0) {

      score -= 10; 

    } else {

      score += s;

    }    

  }

  return (goal.length * 26) - score;

}

​

class DNA {

  constructor(length, mutationRate, mutationAmt) {

    this.length = length;

    this.mutationRate = mutationRate;

    this.mutationAmt = mutationAmt;

    this.dna = new Array(length);

    this.randomise();

  }

  randomise() {

    for(let i = 0; i < this.length; i ++) {

      this.dna[i] = random();

    }

  }

  setDNA(dna) {

    for(let i = 0; i < this.length; i ++) {

      const n = i >= dna.length ? 0 : dna[i];

      this.dna[i] = n;

    }

  }

  duplicate() {

    const newDNA = new DNA(this.length, this.mutationRate, this.mutationAmt);

    newDNA.setDNA(this.dna);

    return newDNA

  }

  mutate() {

    for(let i = 0; i < this.length; i ++) {

      if(random() < this.mutationRate) {

        const amt = random(-this.mutationAmt, this.mutationAmt);

        const n = this.dna[i] + amt;

        this.dna[i] = constrain(n, 0, 1);

      }

    }

  }

  breed(other) {

    const offspring = this.duplicate();

    for(let i = 0; i < this.length; i ++) {

      const n1 = i >= other.dna.length ? 0 : other.dna[i];

      const n2 = this.dna[i];

      offspring.dna[i] = random() < 0.5 ? n1 : n2;

    }

    offspring.mutate();

    return offspring;

  }

}