Day 5: If You Give a Seed a Fertilizer

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  • AtegonOPM
    5•1 year ago

    [JavaScript] Well that was by far the hardest out of all of the days, part 1 was relatively fine but part 2 took me awhile of trying different things

    Ended up solving it by working backwards by trying different location values and seeing if that can become a valid seed. Takes around 3 secs to compute the answer.

    Link to code

    Part 1 Code Block 
    // Part 1
// ======

function part1(input) {
  const split = input.split("\r\n\r\n");

  let pastValues = split[0].match(/\d+/g).map((x) => parseInt(x));
  let currentValues = [];

  for (const section of split.slice(1)) {
    for (const line of section.split("\r\n")) {
      const values = line.match(/\d+/g)?.map((x) => parseInt(x));

      if (!values) {
        continue;
      }

      const sourceStart = values[1];
      const destinationStart = values[0];
      const length = values[2];

      for (let i = 0; i < pastValues.length; i++) {
        if (
          pastValues[i] >= sourceStart &&
          pastValues[i] < sourceStart + length
        ) {
          currentValues.push(destinationStart + pastValues[i] - sourceStart);
          pastValues.splice(i, 1);
          i--;
        }
      }
    }

    for (let i = 0; i < pastValues.length; i++) {
      currentValues.push(pastValues[i]);
    }

    pastValues = [...currentValues];
    currentValues = [];
  }

  return Math.min(...pastValues);
}
    Part 2 Code Block 
    // Part 2
// ======

function part2(input) {
  const split = input.split("\r\n\r\n");

  let seeds = split[0].match(/\d+/g).map((x) => parseInt(x));
  seeds = seeds
    .filter((x, i) => i % 2 == 0)
    .map((x, i) => [x, seeds[i * 2 + 1]]);

  const maps = split
    .slice(1)
    .map((x) => {
      const lines = x.split("\r\n");
      return lines
        .map((x) => x.match(/\d+/g)?.map((x) => parseInt(x)))
        .filter((x) => x);
    })
    .reverse();

  for (let i = 0; true; i++) {
    let curValue = i;

    for (const map of maps) {
      for (const line of map) {
        const sourceStart = line[1];
        const destinationStart = line[0];
        const length = line[2];

        if (
          curValue >= destinationStart &&
          curValue < destinationStart + length
        ) {
          curValue = sourceStart + curValue - destinationStart;
          break;
        }
      }
    }

    for (const [seedRangeStart, seedRangeLength] of seeds) {
      if (
        curValue >= seedRangeStart &&
        curValue < seedRangeStart + seedRangeLength
      ) {
        return i;
      }
    }
  }
}
    • cacheson
      1•1 year ago

      Ended up solving it by working backwards by trying different location values and seeing if that can become a valid seed.

      Huh, that’s clever.

      • AtegonOPM
        1•1 year ago

        Turns out I got really lucky and my location value is much lower than most peoples which is why it can be solved relatively quickly

    • lwhjp
      1•1 year ago

      Torn between doing the problem backwards and implementing a more general case – glad to know both approaches work out in the end!