subtree(users/wpcarro): docking briefcase at '24f5a642' r/3226

git-subtree-dir: users/wpcarro
git-subtree-mainline: 464bbcb15c09813172c79820bcf526bb10cf4208
git-subtree-split: 24f5a642af3aa1627bbff977f0a101907a02c69f
Change-Id: I6105b3762b79126b3488359c95978cadb3efa789

1 files changed, 13 insertions, 0 deletions

diff --git a/users/wpcarro/scratch/facebook/recursion-and-dynamic-programming/permutations.py b/users/wpcarro/scratch/facebook/recursion-and-dynamic-programming/permutations.py
new file mode 100644
index 0000000000..e23972d418
--- /dev/null
+++ b/users/wpcarro/scratch/facebook/recursion-and-dynamic-programming/permutations.py
@@ -0,0 +1,13 @@
+def char_and_rest(i, xs):
+    return xs[i], xs[:i] + xs[i+1:]
+
+# perms :: String -> [String]
+def perms(xs):
+    if len(xs) == 1:
+        return [xs]
+    result = []
+    for c, rest in [char_and_rest(i, xs) for i in range(len(xs))]:
+        result += [c + perm for perm in perms(rest)]
+    return result
+
+print(perms("cat"))