# Python Program for KMP Algorithm for Pattern Searching[duplicate]

• Last Updated : 17 Dec, 2021

## Python

 `# 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 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)`` ` `# This code is contributed by Bhavya Jain`

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