Find largest island in a matrix

MatrixIslands.sc

val matrix = Array(
  Array(0, 1, 0, 0, 1),
  Array(0, 1, 1, 1, 1),
  Array(1, 0, 1, 1, 0),
  Array(1, 1, 0, 0, 1)
)

val rows = matrix.indices
val columns = matrix(0).indices

def getIslandSize(i: Int, j: Int): Int = {
  if (!rows.contains(i) || !columns.contains(j) || matrix(i)(j) == 0) {
    0
  } else {
    matrix(i)(j) = 0
    1 + getIslandSize(i - 1, j) +
      getIslandSize(i, j - 1) +
      getIslandSize(i + 1, j) +
      getIslandSize(i, j + 1)
  }
}

val islandSizes = for {
  i <- rows
  j <- columns
  if matrix(i)(j) == 1
} yield getIslandSize(i, j)

islandSizes.max