aoc2020 day12.js

function boatp1()
{
  let input = document.querySelector('pre').innerHTML.trim().split('\n');
  
  let facing = 'E';
  
  function turn(dir, face, deg)
  {
    let directions = ['E', 'S', 'W', 'N'];
    let change = deg / 90;
    let curi = directions.indexOf(face);
    if(dir == 'L')
    {
      change = change * -1;
    }
    curi += change;
    if(curi < 0)
    {
      curi = directions.length + curi;
    }
    else if(curi >= directions.length)
    {
      curi = curi - directions.length;
    }
    
    return directions[curi];
  }
  
  let [e, n] = input.reduce((out, ins) =>
  {
    let [E, N] = out;
    let [_, dir, amt] = ins.match(/(\w)(\d+)/);
    if(dir == 'R' || dir == 'L')
    {
      facing = turn(dir, facing, amt);
    }
    else
    {
      if(dir == 'F')
      {
        dir = facing;	
      }
      
      switch(dir)
      {
        case 'E':
          E += parseInt(amt, 10);
          break;
        case 'W':
          E -= parseInt(amt, 10);
          break;
        case 'N':
          N += parseInt(amt, 10);
          break;
        case 'S':
          N -= parseInt(amt, 10);
          break;
      }
    }
    
    return [E, N];
  }, [0,0]);
  
  return Math.abs(e) + Math.abs(n);
}

function boatp2()
{
  let input =  document.querySelector('pre').innerHTML.trim().split('\n');
  
  function turn(wE, wN, dir, amt)
  {
    let times = amt/90;
    for(let i = 0; i < times; i++)
    {
      if(dir == 'R')
      {
        [wE, wN] = [wN, -1*wE];        
      }
      else
      {
        [wE, wN] = [-1*wN, wE];
      }
    }
    return [wE, wN];
  }
  
  let [e, n, we, wn] = input.reduce((out, ins) =>
  {
    let [E, N, wE, wN] = out;
    let [_, dir, amt] = ins.match(/(\w)(\d+)/);
    amt = parseInt(amt, 10);
    if(dir == 'R' || dir == 'L')
    {
      [wE, wN] = turn(wE, wN, dir, amt);
    }
    if(dir == 'F')
    {
      N += wN*amt;
      E += wE*amt;
    }
    else
    {
      switch(dir)
      {
        case 'E':
          wE += amt;
          break;
        case 'S':
          wN -= amt;
          break;
        case 'W':
          wE -= amt;
          break;
        case 'N':
          wN += amt;
          break;
      }
    }
    
    return [E, N, wE, wN];
  }, [0,0,10,1]);
  
  return Math.abs(e) + Math.abs(n);
}