Create KMPMatching.py

allalgorithms/string/KMPMatching.py

@@ -0,0 +1,63 @@
+# Python program for KMP Algorithm
+# Written by Bhavya Jain
+# Updated to Python3 syntax by Kenneth Nero
+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) 
+
+