AOC 2023: Problem 13

aoc.ts

const parsed = input.split(`\n\n`);

const start = performance.now();

// ===========================================================
// PART 1
// ===========================================================

let answer1 = 0;

/** Number of characters different between string arrays. */
const diff = (a: string[], b: string[]): number => {
  let diffs = 0;
  for (let i = 0; i < a.length; i++) {
    if (a[i] !== b[i]) diffs++;
  }
  return diffs;
};

/** Returns the the row where the reflection happens, and the total differences = smudge */
function getReflection(grid: string[][], smudge: number): number {
  rLoop: for (let r = 0; r < grid.length - 1; r++) {
    let diffs = diff(grid[r], grid[r + 1]);
    if (diffs <= smudge) {
      const rowsBelow = r;
      const rowsAbove = grid.length - r;
      for (let i = 0; i < Math.min(rowsBelow, rowsAbove); i++) {
        const lowRow = r - i - 1;
        const highRow = r + 2 + i;
        if (lowRow < 0 || highRow >= grid.length) break;
        diffs += diff(grid[lowRow], grid[highRow]);
        if (diffs > smudge) continue rLoop;
      }
      if (diffs === smudge) {
        return r + 1;
      }
    }
  }
  return 0;
}

for (const gridInput of parsed) {
  const grid = parse2d(gridInput);
  const transposed = transpose2d(grid);
  const vertical = getReflection(transposed, 0);
  const horizontal = getReflection(grid, 0);
  answer1 += 100 * horizontal + vertical;
}

console.info(`Answer1: ${answer1} after ${(performance.now() - start).toFixed(2)}ms`);

// ===========================================================
// PART 2
// ===========================================================

let answer2 = 0;

for (const gridInput of parsed) {
  const grid = parse2d(gridInput);
  const transposed = transpose2d(grid);
  const vertical = getReflection(transposed, 1);
  const horizontal = getReflection(grid, 1);
  answer2 += 100 * horizontal + vertical;
}

console.info(`Answer2: ${answer2} after ${(performance.now() - start).toFixed(2)}ms`);