// Daniel Shiffman

// http://natureofcode.com

​

// Genetic Algorithm, Evolving Shakespeare

​

// A class to describe a pseudo-DNA, i.e. genotype

//   Here, a virtual organism's DNA is an array of character.

//   Functionality:

//      -- convert DNA into a string

//      -- calculate DNA's "fitness"

//      -- mate DNA with another set of DNA

//      -- mutate DNA

​

function newChar() {

  let c = floor(random(63, 122));

  if (c === 63) c = 32;

  if (c === 64) c = 46;

​

  return String.fromCharCode(c);

}

​

// Constructor (makes a random DNA)

class DNA {

  constructor(num) {

    // The genetic sequence

    this.genes = [];

    this.fitness = 0;

    for (let i = 0; i < num; i++) {

      this.genes[i] = newChar(); // Pick from range of chars

    }

  }

​

  // Converts character array to a String

  getPhrase() {

    return this.genes.join("");

  }

​

  // Fitness function (returns floating point % of "correct" characters)

  calcFitness(target) {

    let score = 0;

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

      if (this.genes[i] == target.charAt(i)) {

        score++;

      }

    }

    this.fitness = score / target.length;

  }

​

  // Crossover

  crossover(partner) {

    // A new child

    let child = new DNA(this.genes.length);

​

    let midpoint = floor(random(this.genes.length)); // Pick a midpoint

​

    // Half from one, half from the other

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

      if (i > midpoint) child.genes[i] = this.genes[i];

      else child.genes[i] = partner.genes[i];

    }

    return child;

  }

​

  // Based on a mutation probability, picks a new random character

  mutate(mutationRate) {

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

      if (random(1) < mutationRate) {

        this.genes[i] = newChar();

      }

    }

  }

}