September 2017 Update

Task/Topswops/Kotlin/topswops.kotlin

@@ -0,0 +1,35 @@
+// version 1.1.2
+
+val best = IntArray(32)
+
+fun trySwaps(deck: IntArray, f: Int, d: Int, n: Int) {
+    if (d > best[n]) best[n] = d
+    for (i in n - 1 downTo 0) {
+        if (deck[i] == -1 || deck[i] == i) break
+        if (d + best[i] <= best[n]) return
+    }
+    val deck2 = deck.copyOf()
+    for (i in 1 until n) {
+        val k = 1 shl i
+        if (deck2[i] == -1) {
+            if ((f and k) != 0) continue
+        }
+        else if (deck2[i] != i) continue
+        deck2[0] = i
+        for (j in i - 1 downTo 0) deck2[i - j] = deck[j]
+        trySwaps(deck2, f or k, d + 1, n)
+    }
+}
+
+fun topswops(n: Int): Int {
+    require(n > 0 && n < best.size)
+    best[n] = 0
+    val deck0 = IntArray(n + 1)
+    for (i in 1 until n) deck0[i] = -1
+    trySwaps(deck0, 1, 0, n)
+    return best[n]
+}
+
+fun main(args: Array<String>) {
+    for (i in 1..10) println("${"%2d".format(i)} : ${topswops(i)}")
+}