2048-moveUpRecursion.js

2048-moveUpRecursion.js

/**
 * @param line Array Old board array
 * @param result New array with new state. Start empty
 * @param lineWithoutZerosMemoized array list of numbers in line without 0
 */
const moveLineUpFirst = (line, result=[], lineWithoutZerosMemoized=null) => {
  const currentIndex = result.length; // The size of result is equals the line index
  if(line.length === currentIndex) return result; // if result are full, return

  const lineWithoutZeros = lineWithoutZerosMemoized || line.filter((n)=>n > 0); // In first iterate, set, in next iterates keep the value
  if (currentIndex >= lineWithoutZeros.length) { // If current iterate is over than numbers without 0
    // Only add 0 in array result
    return moveLineUpFirst(line, [...result, 0], lineWithoutZeros);
  }

  if (lineWithoutZeros[currentIndex] === lineWithoutZeros[currentIndex + 1]) { // If equals next number
    const total = lineWithoutZeros[currentIndex] + lineWithoutZeros[currentIndex + 1]; // sum
    // Add sum in result and remove the first number in lineWithoutZeros (because the blocks joined in one)
    return moveLineUpFirst(line, [...result, total], lineWithoutZeros.slice(1));
  }

  // Add number in result and call again
  const newNumber = lineWithoutZeros[currentIndex];
  return moveLineUpFirst(line, [...result, newNumber], lineWithoutZeros);
};

const board = [
  [2, 0, 4, 2],
  [0, 0, 4, 4],
  [2, 2, 2, 2],
  [2, 16, 16, 0]
];

console.log(board.map(line => moveLineUpFirst(line)));

/**
[
 [ 2, 4, 2, 0 ],
 [ 8, 0, 0, 0 ],
 [ 4, 4, 0, 0 ],
 [ 2, 32, 0, 0 ]
]
 */