Discussion on: Advent of Code 2020 Solution Megathread - Day 9: Encoding Error

function findWeaknessp2()
{
  let input = document.querySelector('pre')
                      .innerHTML
                      .split('\n')
                      .map(n => parseInt(n, 10));

  let win = 25;
  let fail = -1;
  let failIndex = -1;

  for(let i = win; i < input.length; i++)
  {
    let target = input[i];
    let options = input.slice(i-win, i);
    let found = options.reduce((val, opt) =>
    {
      if(val == -1)
      {
        val = options.indexOf(target-opt);
      }

      return val;
    },-1);

    if(found == -1)
    {
      fail = target;
      failIndex = i;
      break;
    }
  }

  let weakness = -1;

  for(let curWin = 2; curWin < failIndex/2; curWin++)
  {
    for(let i = 0; i < failIndex; i++)
    {
      let options = input.slice(i, i+curWin);
      let testVal = options.reduce((sum, val) => sum+val, 0);
      if(testVal == fail)
      {
        weakness = Math.min(...options) + Math.max(...options);
        break;
      }
    }

    if(weakness > -1)
    {
      break;
    }
  }

  return weakness;
}