Create kmpalgo.py

Author: srinijadharani

DSA/kmpalgo.py

@@ -0,0 +1,59 @@
+# Python program for KMP Algorithm
+def KMPSearch(pat, txt):
+	M = len(pat)
+	N = len(txt)
+
+	# create lps[] that will hold the longest prefix suffix
+	# values for pattern
+	lps = [0]*M
+	j = 0 # index for pat[]
+
+	# Preprocess the pattern (calculate lps[] array)
+	computeLPSArray(pat, M, lps)
+
+	i = 0 # index for txt[]
+	while i < N:
+		if pat[j] == txt[i]:
+			i += 1
+			j += 1
+
+		if j == M:
+			print ("Found pattern at index", str(i-j))
+			j = lps[j-1]
+
+		# mismatch after j matches
+		elif i < N and pat[j] != txt[i]:
+			# Do not match lps[0..lps[j-1]] characters,
+			# they will match anyway
+			if j != 0:
+				j = lps[j-1]
+			else:
+				i += 1
+
+def computeLPSArray(pat, M, lps):
+	len = 0 # length of the previous longest prefix suffix
+
+	lps[0] # lps[0] is always 0
+	i = 1
+
+	# the loop calculates lps[i] for i = 1 to M-1
+	while i < M:
+		if pat[i]== pat[len]:
+			len += 1
+			lps[i] = len
+			i += 1
+		else:
+			# This is tricky. Consider the example.
+			# AAACAAAA and i = 7. The idea is similar
+			# to search step.
+			if len != 0:
+				len = lps[len-1]
+
+				# Also, note that we do not increment i here
+			else:
+				lps[i] = 0
+				i += 1
+
+txt = "ABABDABACDABABCABAB"
+pat = "ABABCABAB"
+KMPSearch(pat, txt)