decodeRailFenceCipher = (string, railCount) => {
  const strLen = string.length;
  const emptyFence = buildFence(railCount);
  const filledFence = fillDecodeFence({
    strLen,
    chars: string.split(''),
    fence: emptyFence,
    targetRail: 0,
    direction: DIRECTIONS.DOWN,
    coords: [0, 0],
  });

  return decodeFence({
    strLen,
    fence: filledFence,
    currentRail: 0,
    direction: DIRECTIONS.DOWN,
    code: [],
  });
}
Decodes the message using Rail Fence Cipher.

@param {string} string - Encoded string
@param {number} railCount - The number of rows in a fence
@returns {string} - Decoded string.