rabincarpnew.py

d = 256

# pat -> pattern
# txt -> text
# q -> A prime number

def search(pat, txt, q):
	M = len(pat)
	N = len(txt)
	i = 0
	j = 0
	p = 0 # hash value for pattern
	t = 0 # hash value for txt
	h = 1

	# The value of h would be "pow(d, M-1)%q"
	for i in xrange(M-1):
		h = (h*d)%q

	# Calculate the hash value of pattern and first window
	# of text
	for i in xrange(M):
		p = (d*p + ord(pat[i]))%q
		t = (d*t + ord(txt[i]))%q

	# Slide the pattern over text one by one
	for i in xrange(N-M+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==t:
			# Check for characters one by one
			for j in xrange(M):
				if txt[i+j] != pat[j]:
					break
				else: j+=1

			# if p == t and pat[0...M-1] = txt[i, i+1, ...i+M-1]
			if j==M:
				print "Pattern found at index " + str(i)

		# Calculate hash value for next window of text: Remove
		# leading digit, add trailing digit
		if i < N-M:
			t = (d*(t-ord(txt[i])*h) + ord(txt[i+M]))%q

			# We might get negative values of t, converting it to
			# positive
			if t < 0:
				t = t+q

# Driver Code
txt = "GEEKS FOR GEEKS"
pat = "GEEK"

# A prime number
q = 101

# Function Call
search(pat,txt,q)

# This code is contributed by Bhavya Jain