advent of code 2020 day 9

woohoo.js

// get the full transmitted data to test
const fullTransmission = ``
  .split("\n")
  .map((input) => parseInt(input));

// This is the number used to generate a sliding window to use as possible inputs
const PREAMBLE_LENGTH = 25;

// Sum to the goal number using only the possible operands
function sumTo(goal, possibleOperands) {
  // return the operands when two operands can combine to the goal number
  return possibleOperands.find((leftOperand) =>
    possibleOperands.some((rightOperand) => leftOperand + rightOperand === goal)
  );
}

// Create a window of size from an array
function* slidingWindow(array, size) {
  let startIndex = 0;
  while (startIndex + size < array.length) {
    yield array.slice(startIndex, startIndex + size);
    startIndex++;
  }
}

// part 1
function getNonSummableNumber(tape, windowLength) {
  // generator to give a window of the window length plus one to get the first number of the next window
  const lengthPlusOne = slidingWindow(tape, windowLength + 1);

  // for each view generated, extract the first number of the next window and see if the number can be summed to
  for (let view of lengthPlusOne) {
    // remove the last number to get the original window length
    const testNumber = view.splice(view.length - 1, 1)[0];
    // if any number in the view fails to combine with another number in the view to equal the test number, return that number
    if (!sumTo(testNumber, view)) {
      return testNumber;
    }
  }
}

// part 2
function getSumContiguousNumbersToTarget(target) {
  const possibleWins = [];
  // check over all numbers
  for (let j = 0; j < fullTransmission.length; j++) {
    const number = fullTransmission[j];
    // for each number, add it to the previous numbers, and check if reached the target
    for (let k = 0; k < possibleWins.length; k++) {
      const win = possibleWins[k];
      if (win && win.numbers && win.total) {
        // keep track of previous numbers and total for each previous number
        win.numbers.push(number);
        win.total += number;
        // woo hoo we reached the target!
        if (win.total === target) {
          // return the sum of the min and max to get the sum
          return Math.min(...win.numbers) + Math.max(...win.numbers);
        }
      }
    }
    possibleWins.push({ numbers: [number], total: number });
  }
}

const nonSummableNumber = getNonSummableNumber(fullTransmission, PREAMBLE_LENGTH);
const contiguousSum = getSumContiguousNumbersToTarget(nonSummableNumber);
console.log(`You've done great, the non summable number found, ${nonSummableNumber} is awesome, and the sum you found ${contiguousSum} is also great!`);

I don't think there is one? I haven't tested anything. I just thought a sliding window would be a fun use of one.

I like the sliding window idea. My part 1 isn't very efficient. Oh well :D

We took a similar approach for part two, but I used .some instead of a for loop.

https://github.com/KevinBatdorf/advent-2020-javascript-challenges/blob/master/day9/day9.js