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, 22 insertions, 0 deletions

diff --git a/users/wpcarro/scratch/data_structures_and_algorithms/string-reverse.py b/users/wpcarro/scratch/data_structures_and_algorithms/string-reverse.py
new file mode 100644
index 000000000000..8b4cdac1c271
--- /dev/null
+++ b/users/wpcarro/scratch/data_structures_and_algorithms/string-reverse.py
@@ -0,0 +1,22 @@
+
+# swap :: Int -> Int -> [Char] -> IO ()
+def swap(ia, iz, xs):
+    # handle swap when ia == iz
+    assert ia <= iz
+    xs[ia], xs[iz] = xs[iz], xs[ia]
+    
+
+# reverse :: [Char] -> IO ()
+def reverse(xs):
+    ia = 0
+    iz = len(xs) - 1
+
+    while ia <= iz:
+        swap(ia, iz, xs)
+        ia += 1
+        iz -= 1
+
+x = list("superduperpooper")
+reverse(x)
+print(x)
+print("Tests pass")