June 2018 Update

Task/Percolation-Bond-percolation/Kotlin/percolation-bond-percolation.kotlin

@@ -0,0 +1,91 @@
+// version 1.2.10
+
+import java.util.Random
+
+val rand = Random()
+const val RAND_MAX = 32767
+
+// cell states
+const val FILL  = 1
+const val RWALL = 2  // right wall
+const val BWALL = 4  // bottom wall
+
+val x = 10
+val y = 10
+var grid = IntArray(x * (y + 2))
+var cells = 0
+var end = 0
+var m = 0
+var n = 0
+
+fun makeGrid(p: Double) {
+    val thresh = (p * RAND_MAX).toInt()
+    m = x
+    n = y
+    grid.fill(0)  // clears grid
+    for (i in 0 until m) grid[i] = BWALL or RWALL
+    cells = m
+    end = m
+    for (i in 0 until y) {
+        for (j in x - 1 downTo 1) {
+            val r1 = rand.nextInt(RAND_MAX + 1)
+            val r2 = rand.nextInt(RAND_MAX + 1)
+            grid[end++] = (if (r1 < thresh) BWALL else 0) or
+                          (if (r2 < thresh) RWALL else 0)
+        }
+        val r3 = rand.nextInt(RAND_MAX + 1)
+        grid[end++] = RWALL or (if (r3 < thresh) BWALL else 0)
+    }
+}
+
+fun showGrid() {
+    for (j in 0 until m) print("+--")
+    println("+")
+
+    for (i in 0..n) {
+        print(if (i == n) " " else "|")
+        for (j in 0 until m) {
+            print(if ((grid[i * m + j + cells] and FILL) != 0) "[]" else "  ")
+            print(if ((grid[i * m + j + cells] and RWALL) != 0) "|" else " ")
+        }
+        println()
+        if (i == n) return
+        for (j in 0 until m) {
+            print(if ((grid[i * m + j + cells] and BWALL) != 0) "+--" else "+  ")
+        }
+        println("+")
+    }
+}
+
+fun fill(p: Int): Boolean {
+    if ((grid[p] and FILL) != 0) return false
+    grid[p] = grid[p] or FILL
+    if (p >= end) return true  // success: reached bottom row
+    return (((grid[p + 0] and BWALL) == 0) && fill(p + m)) ||
+           (((grid[p + 0] and RWALL) == 0) && fill(p + 1)) ||
+           (((grid[p - 1] and RWALL) == 0) && fill(p - 1)) ||
+           (((grid[p - m] and BWALL) == 0) && fill(p - m))
+}
+
+fun percolate(): Boolean {
+    var i = 0
+    while (i < m && !fill(cells + i)) i++
+    return i < m
+}
+
+fun main(args: Array<String>) {
+    makeGrid(0.5)
+    percolate()
+    showGrid()
+
+    println("\nrunning $x x $y grids 10,000 times for each p:")
+    for (p in 1..9) {
+        var cnt = 0
+        val pp = p / 10.0
+        for (i in 0 until 10_000) {
+            makeGrid(pp)
+            if (percolate()) cnt++
+        }
+        println("p = %3g: %.4f".format(pp, cnt.toDouble() / 10_000))
+    }
+}