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Challenge #9: 🚂 The magic train

Level: 🟠 MEDIUM

Instructions

The elves are playing with a magical train 🚂 that carries gifts. This train moves on a board represented by an array of strings.

The train consists of an engine (@), followed by its carriages (o), and must collect magical fruits (*) which serve as fuel. The movement of the train follows these rules:

You will receive two parameters board and mov.

board is an array of strings that represents the board:

  • @ is the train's engine.
  • o are the train's carriages.
  • * is a magical fruit.
  • · are empty spaces.

mov is a string that indicates the next movement of the train from the train's head @:

  • 'L': left
  • 'R': right
  • 'U': up
  • 'D': down.

With this information, you must return a string:

  • 'crash': If the train crashes into the edges of the board or itself.
  • 'eat': If the train collects a magical fruit (*).
  • 'none': If it moves without crashing or collecting any magical fruit.

Examples:

const board = ['·····', '*····', '@····', 'o····', 'o····']

console.log(moveTrain(board, 'U'))
// ➞ 'eat'
// Because the train moves up and finds a magical fruit

console.log(moveTrain(board, 'D'))
// ➞ 'crash'
// The train moves down and the head crashes into itself

console.log(moveTrain(board, 'L'))
// ➞ 'crash'
// The train moves to the left and crashes into the wall

console.log(moveTrain(board, 'R'))
// ➞ 'none'
// The train moves to the right and there is empty space on the right

Solutions

  • JavaScript

    function moveTrain(board, mov) {
  const x = board.findIndex(row => row.includes('@'))
  const y = board[x].indexOf('@')

  const result = {'*': 'eat', '·': 'none', 'o': 'crash', undefined: 'crash'}
  const moves = {U: [x - 1, y], D: [x + 1, y], L: [x, y - 1], R: [x, y + 1]}
  const [dx, dy] = moves[mov]

  return result[board[dx]?.[dy]]
}

  • TypeScript

    type Space = '·' | '@' | '*' | 'o'
type Board = Space[]
type Movement = 'U' | 'D' | 'R' | 'L'
type Result = 'none' | 'crash' | 'eat'

function moveTrain(board: Board, mov: Movement): Result {
  const x: number = board.findIndex((row: string) => row.includes('@'))
  const y: number = board[x].indexOf('@')
  const result = {'*': 'eat', '·': 'none', 'o': 'crash', undefined: 'crash'}
  const moves = {U: [x - 1, y], D: [x + 1, y], L: [x, y - 1], R: [x, y + 1]}
  const [dx, dy] = moves[mov]
  return result[board[dx]?.[dy]]
}

  • Python

    def move_train(board: List[str], mov: Literal['U', 'D', 'R', 'L']) -> Literal['none', 'crash', 'eat']:
  x = next(i for i, row in enumerate(board) if '@' in row)
  y = board[x].index('@')

  moves = {
    'U': (x - 1, y),
    'D': (x + 1, y),
    'R': (x, y + 1),
    'L': (x, y - 1)
  }
  result = {
    '*': 'eat',
    '·': 'none',
    'o': 'crash'
  }

  new_x, new_y = moves[mov]

  try:
    return result[board[new_x][new_y]]
  except IndexError:
    return 'crash'