tasks a-s

Task/Permutations-Derangements/Groovy/permutations-derangements-1.groovy

@@ -0,0 +1,9 @@
+def fact = { n -> [1,(1..<(n+1)).inject(1) { prod, i -> prod * i }].max() }
+def subfact
+subfact = { BigInteger n -> (n == 0) ? 1 : (n == 1) ? 0 : ((n-1) * (subfact(n-1) + subfact(n-2))) }
+
+def derangement = { List l ->
+    def d = []
+    l.eachPermutation { p -> if ([p,l].transpose().every{ it[0] != it[1] }) d << p }
+    d
+}

Task/Permutations-Derangements/Groovy/permutations-derangements-2.groovy

@@ -0,0 +1,16 @@
+def d = derangement([1,2,3,4])
+assert d.size() == subfact(4)
+d.each { println it }
+
+println """
+n   # derangements   subfactorial
+=   ==============   ============"""
+(0..9). each { n ->
+    def dr = derangement((1..<(n+1)) as List)
+    def sf = subfact(n)
+    printf('%1d   %14d   %12d\n', n, dr.size(), sf)
+}
+
+println """
+!20 == ${subfact(20)}
+"""