PercoScala

/* An attempt to make Percolation.java more functional but possibly not the best example as Array is preferred here over other immutable collections
Scala code remains very imperative...some conciseness gained but that's it */

import edu.princeton.cs.algs4.WeightedQuickUnionUF

/* primary constructor shorthand, n parameter without val or var
 are private values so not accessible from the
 outside and immutable*/

class PercoScala(n: Int) {
  // default member visibility is public
  val grid_size: Int = n * n
  val wquf: WeightedQuickUnionUF = new WeightedQuickUnionUF(grid_size + 2)
  val top = 0
  val bottom: Int = grid_size + 1

  // Arrays as size is fixed and fast random access important
  val isSiteOpen: Array[Boolean] = new Array[Boolean](grid_size + 2)

  // top is always open
  isSiteOpen(top) = true
  isSiteOpen(bottom) = true

  // var are just simple enough for a global counter
  var openSites: Int = 0

  def validate(i: Int, j: Int) =
    if (i <= 0 || i > n || j <= 0 || j > n) throw new IllegalArgumentException(
      "indices (" + i + "," + j + ") are not between 1 and " + n)

  def xyTo1D(i: Int, j: Int) = j + n * (i - 1)

   def open(i: Int, j: Int) = {
    validate(i, j)
    val site = xyTo1D(i, j)
    if (!isSiteOpen(site)) {
      isSiteOpen(site) = true
      openSites += 1
      connectAdjacentSites(i, j)
    }
  }

  def connectAdjacentSites(i: Int, j: Int): Unit = {
    val site = xyTo1D(i, j)

    // connect to top sites on the first row
    if (i == 1) wquf.union(site, top)

    // above site exits only if i>1
    if (i > 1) {
      val adjacent = xyTo1D(i - 1, j)
      if (isSiteOpen(adjacent)) wquf.union(site, adjacent)
    }

    // left site
    if (j > 1 && j <= n) {
      val adjacent = xyTo1D(i, j - 1)
      if (isSiteOpen(adjacent)) wquf.union(site, adjacent)
    }

    // right site
    if (j >= 1 && j < n) {
      val adjacent = xyTo1D(i, j + 1)
      if (isSiteOpen(adjacent)) wquf.union(site, adjacent)
    }


    // below site exists only if i<n
    if (i != n) {
      val adjacent = xyTo1D(i + 1, j)
      if (isSiteOpen(adjacent)) wquf.union(site, adjacent)
    }

    // all bottom sites are connected to bottom !
    if (i == n) wquf.union(site, bottom);

  }

  def isOpen(i: Int, j: Int) = isSiteOpen(xyTo1D(i, j))

  def isFull(i: Int, j: Int) = wquf.connected(xyTo1D(i, j), 0)

  def numberOfOpenSites = openSites

  def percolates = wquf.connected(top, bottom)


}