September 2017 Update

Task/Permutations/R/permutations-2.r

@@ -0,0 +1,11 @@
+# list of the vectors by inserting x in s at position 0...end.
+linsert <- function(x,s) lapply(0:length(s), function(k) append(s,x,k))
+
+# list of all permutations of 1:n
+perm <- function(n){
+    if (n == 1) list(1)
+    else unlist(lapply(perm(n-1), function(s) linsert(n,s)),
+                recursive = F)}
+
+# permutations of a vector s
+permutation <- function(s) unique(lapply(perm(length(s)), function(i) s[i]))

Task/Permutations/R/permutations-3.r

@@ -0,0 +1,18 @@
+> permutation(letters[1:3])
+[[1]]
+[1] "c" "b" "a"
+
+[[2]]
+[1] "b" "c" "a"
+
+[[3]]
+[1] "b" "a" "c"
+
+[[4]]
+[1] "c" "a" "b"
+
+[[5]]
+[1] "a" "c" "b"
+
+[[6]]
+[1] "a" "b" "c"