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

git-subtree-dir: users/wpcarro
git-subtree-mainline: 464bbcb15c
git-subtree-split: 24f5a642af
Change-Id: I6105b3762b79126b3488359c95978cadb3efa789

users/wpcarro/scratch/facebook/hard/binary-adder.py

@@ -0,0 +1,22 @@
+import random
+
+def add(a, b):
+    """
+    Return the sum of `a` and `b`.
+    """
+    if b == 0:
+        return a
+    sum = a ^ b
+    carry = (a & b) << 1
+    return add(sum, carry)
+
+################################################################################
+# Tests
+################################################################################
+
+for _ in range(10):
+    x, y = random.randint(0, 100), random.randint(0, 100)
+    print("{} + {} = {} == {}".format(x, y, x + y, add(x, y)))
+    assert add(x, y) == x + y
+    print("Pass!")
+print("Success!")