Advent of Code 2019 Day 16

advent2019-16.1.js

‎‎​const FFT = (input, maxPhase) => {
    let data = input.split('').map(i => parseInt(i));
  
    for (let phase = 0; phase < maxPhase; phase++) {
      let newData = [];
  
      for (let X = 0; X < input.length; X++) {
        let newVal = 0;
        for (let Y = X; Y < input.length; Y++) {
          switch (~~((Y + 1) / (X + 1)) % 4) {
            case 1: newVal += data[Y]; break;
            case 3: newVal -= data[Y]; break;
          }
        }
        newData.push(Math.abs(newVal) % 10);
      }
      data = newData;
    }
  
    return data.join('');
  }
  
  [
    ['12345678', 4, '01029498'],
    ['80871224585914546619083218645595', 100, '24176176'],
    ['19617804207202209144916044189917', 100, '73745418'],
    ['69317163492948606335995924319873', 100, '52432133']
  ].forEach((i,x) => {
    let result = FFT(i[0], i[1]);
    console.assert(result.substr(0, i[2].length) === i[2], `Fail test #${x} (got ${result}, expected starting with ${i[2]})`);
  });
  
  let bigData = '59709511599794439805414014219880358445064269099345553494818286560304063399998657801629526113732466767578373307474609375929817361595469200826872565688108197109235040815426214109531925822745223338550232315662686923864318114370485155264844201080947518854684797571383091421294624331652208294087891792537136754322020911070917298783639755047408644387571604201164859259810557018398847239752708232169701196560341721916475238073458804201344527868552819678854931434638430059601039507016639454054034562680193879342212848230089775870308946301489595646123293699890239353150457214490749319019572887046296522891429720825181513685763060659768372996371503017206185697';
  console.log(FFT(bigData, 100).substr(0, 8));