advent-code-2021-day-11.js

let input = `5483143223
2745854711
5264556173
6141336146
6357385478
4167524645
2176841721
6882881134
4846848554
5283751526`;

let w = 10,
  h = 10;

let darkest = -Number.MAX_SAFE_INTEGER;
function run() {
  let matrix = input
    .split("\n")
    .filter(Boolean)
    .map((row) => row.split("").map((c) => +c));

  // padding for one addition row/column with zeros
  function padding() {
    matrix.unshift(Array(w).fill(darkest));
    matrix.push(Array(w).fill(darkest));
    matrix = matrix.map((row) => [darkest, ...row, darkest]);
  }
  padding();

  function step(matrix) {
    /**
     * @type number[][]
     */
    let newMatrix = JSON.parse(JSON.stringify(matrix));
    for (let y = 1; y < h + 2; y++) {
      for (let x = 1; x < w + 2; x++) {
        newMatrix[y][x]++;
      }
    }

    let newFlash = false;
    do {
      newFlash = false;
      for (let y = 1; y < h + 2; y++) {
        for (let x = 1; x < w + 2; x++) {
          if (newMatrix[y][x] === 10) {
            newMatrix[y][x]++;
            for (let i = -1; i < 2; i++) {
              for (let j = -1; j < 2; j++) {
                if (i === 0 && j === 0) {
                  continue;
                }
                if (newMatrix[y + i][x + j] <= 9) {
                  newMatrix[y + i][x + j]++;
                  if (newMatrix[y + i][x + j] === 10) {
                    newFlash = true;
                  }
                }
              }
            }
          }
        }
      }
    } while (newFlash);

    let counts = 0;
    // count how many flashed and reset
    for (let y = 1; y < h + 2; y++) {
      for (let x = 1; x < w + 2; x++) {
        if (newMatrix[y][x] > 9) {
          counts++;
          newMatrix[y][x] = 0;
        }
      }
    }
    return [newMatrix, counts];
  }

  for (let i = 0; ; i++) {
    let [newMatrix, counts] = step(matrix);
    totalCounts += counts;
    matrix = newMatrix;
    if (counts === 100) {
      console.log(i);
      break;
    }
  }
}

run();