Knot Hash - Advent of Code - 20171210

ac20171210.js

let knotHash = function(size, lengths) {
  let numbers = new Array(size).fill(0).map((v, i) => i);
  let skip = 0;
  let currentPosition = 0;

  lengths.forEach((v, i) => {
    let length = [...numbers, ...numbers]
      .slice(currentPosition, currentPosition + v)
      .reverse();
    length.forEach((v, i) => {
      numbers[(currentPosition + i) % numbers.length] = v;
    });
    currentPosition = (currentPosition + v + skip++) % numbers.length;
  });

  return numbers[0] * numbers[1];
};

let knotHashRounds = function(lengths) {
  let salt = [17, 31, 73, 47, 23];

  let skip = 0;
  let currentPosition = 0;
  let numbers = new Array(256).fill(0).map((v, i) => i);

  let knotHash = function(input, lengths) {
    let numbers = input.slice();
    lengths.forEach((v, i) => {
      let length = [...numbers, ...numbers]
        .slice(currentPosition, currentPosition + v)
        .reverse();
      length.forEach((v, i) => {
        numbers[(currentPosition + i) % numbers.length] = v;
      });
      currentPosition = (currentPosition + v + skip++) % numbers.length;
    });

    return numbers;
  };

  lengths = lengths
    .split('')
    .map(v => v.charCodeAt())
    .concat(salt);
  for (let i = 0; i < 64; i++) {
    numbers = knotHash(numbers, lengths);
  }

  let denseHash = numbers.reduce((acc, v, i) => {
    let index = Math.floor(i / 16);
    acc[index] = acc[index] ^ v;
    return acc;
  }, new Array(16).fill(0));
  denseHash = denseHash.map(v => ('0' + v.toString(16)).substr(-2)).join('');

  return denseHash;
};

let test = [3, 4, 1, 5];
let size = 5;
test = [63, 144, 180, 149, 1, 255, 167, 84, 125, 65, 188, 0, 2, 254, 229, 24];
size = 256;
let result = knotHash(size, test);
console.log(result);

test = '63,144,180,149,1,255,167,84,125,65,188,0,2,254,229,24';
result = knotHashRounds(test);
console.log(result);
// 7e81 4e31 206f 4073 fe25 7cb9 50fd 4807
// 62e2 204d 2ca4 f492 4f6e 7a80 f128 8786