aoc2021_day14_part2.js

(function(inp)
{
  let [polymer, rest] = inp.split('\n\n');
  
  let pairInserts = new Map(rest.trim().split('\n').map(line => line.split(' -> ')));
  
  let pairCounts = new Map();
   
  let initialPairs = polymer.split('').reduce((acc, s, i, arr) =>
  {
    if(i < arr.length - 1)
    {
      acc.push(s+arr[i+1]);
    }
    return acc;
  }, []);
  
  let lastElement = polymer[polymer.length -1];
  
  for(let pair of initialPairs)
  {
    pairCounts.set(pair, 1);
  }
  
  for(let i = 0; i < 40; i++)
  {
	  let newPairCounts = new Map();

    for(let [pair, count] of pairCounts)
    {
      let [l, r] = pair.split('');
      let insert = pairInserts.get(pair);
      let leftPair = l + insert;
      if(newPairCounts.has(leftPair))
      {
        let oc = newPairCounts.get(leftPair);
        newPairCounts.set(leftPair, oc+count);
      }
      else
      {
        newPairCounts.set(leftPair, count);
      }
      let rightPair = insert + r;
      if(newPairCounts.has(rightPair))
      {
        let oc = newPairCounts.get(rightPair);
        newPairCounts.set(rightPair, oc+count);
      }
      else
      {
        newPairCounts.set(rightPair, count);
      }
    }
    
    pairCounts = newPairCounts;
  }
  
  let elCounts = new Map();
  
  for(let [pair, count] of pairCounts)
  {
    let el = pair[0];
    if(elCounts.has(el))
    {
      let c = elCounts.get(el);
      elCounts.set(el, c + count);
    }
    else
    {
      elCounts.set(el, count);
    }
  }
  
  if(elCounts.has(lastElement))
  {
    let c = elCounts.get(lastElement);
    elCounts.set(lastElement, c + 1);
  }
  else
  {
    elCounts.set(lastElement, 1);
  }
  
  let max = 0;
  let min = Number.MAX_SAFE_INTEGER;
  
  for(let [el, count] of elCounts)
  {
    if(count < min)
    {
      min = count;
    }
    
    if(count > max)
    {
      max = count;
    }
  }
  
  return max - min;
})(document.querySelector('pre').textContent);