fixed failure function and cleaned up code in kmp + added rabin-karp

strings/rabin-karp.py

@@ -0,0 +1,50 @@
+def rabin_karp(pattern, text):
+    """
+
+    The Rabin-Karp Algorithm for finding a pattern within a piece of text
+    with complexity O(nm), most efficient when it is used with multiple patterns
+    as it is able to check if any of a set of patterns match a section of text in o(1) given the precomputed hashes.
+
+    This will be the simple version which only assumes one pattern is being searched for but it's not hard to modify
+
+    1) Calculate pattern hash
+
+    2) Step through the text one character at a time passing a window with the same length as the pattern
+        calculating the hash of the text within the window compare it with the hash of the pattern. Only testing
+        equality if the hashes match
+
+    """
+    p_len = len(pattern)
+    p_hash = hash(pattern)
+
+    for i in range(0, len(text) - (p_len - 1)):
+
+        # written like this t
+        text_hash = hash(text[i:i + p_len])
+        if text_hash == p_hash and \
+                text[i:i + p_len] == pattern:
+            return True
+    return False
+
+
+if __name__ == '__main__':
+    # Test 1)
+    pattern = "abc1abc12"
+    text1 = "alskfjaldsabc1abc1abc12k23adsfabcabc"
+    text2 = "alskfjaldsk23adsfabcabc"
+    assert rabin_karp(pattern, text1) and not rabin_karp(pattern, text2)
+
+    # Test 2)
+    pattern = "ABABX"
+    text = "ABABZABABYABABX"
+    assert rabin_karp(pattern, text)
+
+    # Test 3)
+    pattern = "AAAB"
+    text = "ABAAAAAB"
+    assert rabin_karp(pattern, text)
+
+    # Test 4)
+    pattern = "abcdabcy"
+    text = "abcxabcdabxabcdabcdabcy"
+    assert rabin_karp(pattern, text)