Spinlock - Advent of Code - 20171217

ac20171217.js

let spinLock_1 = function(step, target) {
  let buffer = [0];
  let position = 0;
  for (let i = 1; i <= target; i++) {
    position = (position + step) % buffer.length;
    buffer.splice(++position, 0, i);
  }

  return buffer[position + 1];
};

let spinLock_2 = function(step, target) {
  let buffer = [0],
    pos = 0;

  for (let i = 1; i <= target; i++) {
    pos = (pos + step + 1) % i;
    buffer = [...buffer.slice(0, pos), i, ...buffer.slice(pos)];
  }
  return buffer[buffer.indexOf(target) + 1];
};

let spinLock = spinLock_1;

let bigSpinLock = function(step, cycles, target) {
  let buffer = [0];
  let position = 0;
  for (let i = 1; i <= cycles; i++) {
    position = (position + step) % i + 1;
    //buffer.splice(++position, 0, i);
    if (position == 1) {
      buffer[position] = i;
    }
  }

  return buffer[1];
};

let test = 304;
let cycles = 2017;
let result = spinLock(test, cycles);
console.log(result);

test = 304;
cycles = 50000000;
result = bigSpinLock(test, cycles);
console.log(result);