1 files changed, 26 insertions, 0 deletions
diff --git a/challenge-277/steven-wilson/python/ch-1.py b/challenge-277/steven-wilson/python/ch-1.py
new file mode 100644
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+++ b/challenge-277/steven-wilson/python/ch-1.py
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+#!/usr/bin/env python3
+
+from collections import Counter
+
+
+def count_common(words1, words2):
+    """ Given  two array of strings, return the count of words that appears in
+    both arrays exactly once.
+
+    >>> count_common(("Perl", "is", "my", "friend"), ("Perl", "and", "Raku", "are", "friend"))
+    2
+    >>> count_common(("Perl", "and", "Python", "are", "very", "similar"), ("Python", "is", "top", "in", "guest", "languages"))
+    1
+    >>> count_common(("Perl", "is", "imperative", "Lisp", "is", "functional"), ("Crystal", "is", "similar", "to", "Ruby"))
+    0
+    """
+    c1 = Counter(words1)
+    c2 = Counter(words2)
+    return len({k for k, v in c1.items() if v == 1} &
+               {k for k, v in c2.items() if v == 1})
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod(verbose=True)