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Returning Index instead of boolean in knuth_morris_pratt (kmp) function, making it compatible with str.find(). (#9083)

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* Update knuth_morris_pratt.py - changed Boolean to Index

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* Update knuth_morris_pratt.py

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* Update knuth_morris_pratt.py

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* Update strings/knuth_morris_pratt.py

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Hetarth Jain 2023-09-28 23:54:46 +05:30 committed by GitHub
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commit 35dd529c85
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1 changed files with 25 additions and 8 deletions
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33
strings/knuth_morris_pratt.py
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@ -1,7 +1,7 @@
from __future__ import annotations from __future__ import annotations
def kmp(pattern: str, text: str) -> bool: def knuth_morris_pratt(text: str, pattern: str) -> int:
""" """
The Knuth-Morris-Pratt Algorithm for finding a pattern within a piece of text The Knuth-Morris-Pratt Algorithm for finding a pattern within a piece of text
with complexity O(n + m) with complexity O(n + m)
@ -14,6 +14,12 @@ def kmp(pattern: str, text: str) -> bool:
2) Step through the text one character at a time and compare it to a character in 2) Step through the text one character at a time and compare it to a character in
the pattern updating our location within the pattern if necessary the pattern updating our location within the pattern if necessary
>>> kmp = "knuth_morris_pratt"
>>> all(
... knuth_morris_pratt(kmp, s) == kmp.find(s)
... for s in ("kn", "h_m", "rr", "tt", "not there")
... )
True
""" """
# 1) Construct the failure array # 1) Construct the failure array
@ -24,7 +30,7 @@ def kmp(pattern: str, text: str) -> bool:
while i < len(text): while i < len(text):
if pattern[j] == text[i]: if pattern[j] == text[i]:
if j == (len(pattern) - 1): if j == (len(pattern) - 1):
return True return i - j
j += 1 j += 1
# if this is a prefix in our pattern # if this is a prefix in our pattern
@ -33,7 +39,7 @@ def kmp(pattern: str, text: str) -> bool:
j = failure[j - 1] j = failure[j - 1]
continue continue
i += 1 i += 1
return False return -1
def get_failure_array(pattern: str) -> list[int]: def get_failure_array(pattern: str) -> list[int]:
@ -57,27 +63,38 @@ def get_failure_array(pattern: str) -> list[int]:
if __name__ == "__main__": if __name__ == "__main__":
import doctest
doctest.testmod()
# Test 1) # Test 1)
pattern = "abc1abc12" pattern = "abc1abc12"
text1 = "alskfjaldsabc1abc1abc12k23adsfabcabc" text1 = "alskfjaldsabc1abc1abc12k23adsfabcabc"
text2 = "alskfjaldsk23adsfabcabc" text2 = "alskfjaldsk23adsfabcabc"
assert kmp(pattern, text1) and not kmp(pattern, text2) assert knuth_morris_pratt(text1, pattern) and knuth_morris_pratt(text2, pattern)
# Test 2) # Test 2)
pattern = "ABABX" pattern = "ABABX"
text = "ABABZABABYABABX" text = "ABABZABABYABABX"
assert kmp(pattern, text) assert knuth_morris_pratt(text, pattern)
# Test 3) # Test 3)
pattern = "AAAB" pattern = "AAAB"
text = "ABAAAAAB" text = "ABAAAAAB"
assert kmp(pattern, text) assert knuth_morris_pratt(text, pattern)
# Test 4) # Test 4)
pattern = "abcdabcy" pattern = "abcdabcy"
text = "abcxabcdabxabcdabcdabcy" text = "abcxabcdabxabcdabcdabcy"
assert kmp(pattern, text) assert knuth_morris_pratt(text, pattern)
# Test 5) # Test 5) -> Doctests
kmp = "knuth_morris_pratt"
assert all(
knuth_morris_pratt(kmp, s) == kmp.find(s)
for s in ("kn", "h_m", "rr", "tt", "not there")
)
# Test 6)
pattern = "aabaabaaa" pattern = "aabaabaaa"
assert get_failure_array(pattern) == [0, 1, 0, 1, 2, 3, 4, 5, 2] assert get_failure_array(pattern) == [0, 1, 0, 1, 2, 3, 4, 5, 2]