Added Rabin Carp(Rolling Hash Algorithm in the Python Directory)

Python/RabinCarp_RollingHash.py

@@ -0,0 +1,65 @@
+# Following program is the python implementation of Rabin Karp Algorithm 
+#The source code has been partly taken from the book of CLRS
+
+# d is the number of characters in the input alphabet
+dmnt = 256
+
+# pat  -> would be pattern
+# txt  -> given text
+# prime_n    -> nth  prime number
+
+
+def search(pat, txt, prime_n):
+    pal_len = len(pat)
+    txt_len = len(txt)
+    st_idx = 0
+    en_idx = 0
+    p_hash = 0    # hash value for search pattern
+    t_hash = 0    # hash value for given  txt
+    h = 1
+
+    # The value of h would be "pow(d, M-1)% q"
+    for st_idx in range(pal_len-1):
+        h = (h * dmnt) % prime_n
+
+    # Calculate the hash value of pattern and first window
+    # of text
+    for st_idx in range(pal_len):
+        p_hash = (dmnt * p_hash + ord(pat[st_idx])) % prime_n
+        t_hash = (dmnt * t_hash + ord(txt[st_idx])) % prime_n
+
+    # Slide the pattern over text one by one
+    for st_idx in range(txt_len-pal_len + 1):
+        # Check the hash values of current window of text and
+        # pattern if the hash values match then only check
+        # for characters on by one
+        if p_hash == t_hash:
+            # Check for characters one by one
+            for en_idx in range(pal_len):
+                if txt[st_idx + en_idx] != pat[en_idx]:
+                    break
+
+            en_idx += 1
+            # if p == t and pat[0...M-1] = txt[i, i + 1, ...i + M-1]
+            if en_idx == pal_len:
+                print("Pattern found at index " + str(st_idx))
+                return
+
+        # Calculate the hash value for next window of text: Remove
+        if st_idx < txt_len-pal_len:
+            t_hash = (dmnt*(t_hash-ord(txt[st_idx])*h) +
+                      ord(txt[st_idx + pal_len])) % prime_n
+
+            # We might get negative values of t, converting it to
+            # positive
+            if t_hash < 0:
+                t_hash = t_hash + prime_n
+    print("No pattern was found")
+    return
+
+
+# Driver program to test the above function
+txt = "some random number isbas nanfsfsa  asjf ajfa fjasbfjkasf as jasfjas af"
+pat = "some3"
+prime_no = 101  # A prime number
+search(pat, txt, prime_no)