Past exam of the year 1 of the computer science course of the University of Oxford / 2022 / Imperative programming (resit) / 5 / b / Solution

class Chomps(N: Int) {
  require(N > 0 && N.toLong * N.toLong <= Int.MaxValue)
  private val height = Array.fill(N)(N)
  private var remaining = (N.toLong * N.toLong).toInt

  def Count(): Int = remaining

  def Legal(x: Int, y: Int): Boolean =
    0 <= x && x < N && 0 <= y && y < height(x)

  def Move(x: Int, y: Int): Unit = {
    require(Legal(x, y), "illegal move")
    var i = x
    while (i < N && height(i) > y) {
      remaining -= height(i) - y
      height(i) = y
      i += 1
    }
  }

  def Display(): Unit = {
    require(N < 10, "single-digit display labels required")
    var y = N - 1
    while (y >= 0) {
      print(y + "  ")
      var x = 0
      while (x < N) {
        print(if (y < height(x)) "* " else "  ")
        x += 1
      }
      println()
      y -= 1
    }
    print("   ")
    var x = 0
    while (x < N) { print(x + " "); x += 1 }
    println()
  }
}