day11.ts

export const runNStepsOfSimultation = (grid: Cell[][], n: number): number => {
  let flashesCount = 0;

  for (let step = 0; step < n; step++) {
    const q: Cell[] = [];

    // Increase all
    grid.forEach((row) => row.forEach(cell => cell.increase()));

    // Add naighbours to queue
    grid.forEach((row) => row.forEach((cell) => {
      if (cell.value === 0) {
        flashesCount++;
        getNonFlashingCellNaighbours(cell, grid).forEach(n => q.unshift(n));
      }
    }))

    while(q.length) {
      const cell = q.pop();
      if (cell.value !== 0) {
        cell.increase();
        if (cell.value === 0) {
          flashesCount++;
          getNonFlashingCellNaighbours(cell, grid).forEach(n => q.unshift(n));
        }
      }
    }
  }

  return flashesCount;
}

export const solveP1 = (input: string) => {
  const grid = parseInput(input);
  // Run simulation for 100 steps
  return runNStepsOfSimultation(grid, 100);
};

export const solveP2 = (input: string) => {
  const grid = parseInput(input);
  let stepCount = 0;

  // Run simulation 1 step at a time until condition is met
  while (true) {
    stepCount++
    runNStepsOfSimultation(grid, 1);

    // Condition: all cells are flashing
    if (grid.every((row) => row.every(col => col.value === 0))) {
      return stepCount;
    }
  }
}

/**
 * UTILITY FUNCTIONS
 */

class Cell {
  value: number;
  row: number;
  col: number;

  constructor(v: number, row: number, col: number) {
    this.value = v;
    this.row = row;
    this.col = col;
  }

  increase() {
    this.value += 1;
    if (this.value > 9) {
      this.value = 0;
    }
  }
}

export const parseInput = (input: string): Cell[][] => {
  return input.trim().split('\n').map((row, rowIdx) => {
    return row.split('').map((v, colIdx) => new Cell(Number(v), Number(rowIdx), Number(colIdx)));
  })
}

const getNonFlashingCellNaighbours = (cell: Cell, grid: Cell[][]): Cell[] => {
  const { row, col } = cell;
  const t = grid[row - 1]?.[col];
  const tr = grid[row - 1]?.[col + 1];
  const r = grid[row]?.[col + 1];
  const br = grid[row + 1]?.[col + 1];
  const b = grid[row + 1]?.[col];
  const bl = grid[row + 1]?.[col - 1];
  const l = grid[row]?.[col - 1];
  const tl = grid[row - 1]?.[col - 1];

  return [t, tr, r, br, b, bl, l, tl].filter(c => !!c && c.value !== 0);
}