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Suffix Array and LCP implementation.py

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Putul Singh 2024-10-19 12:39:41 +05:30 committed by GitHub
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1 changed files with 13 additions and 24 deletions
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divide_and_conquer/Suffix Array and LCP implementation.py
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@ -21,13 +21,15 @@ class SuffixArray:
[5, 3, 1, 0, 4, 2] [5, 3, 1, 0, 4, 2]
""" """
n = len(self.text) n = len(self.text)
suffixes = sorted(range(n), key=lambda i: self.text[i:]) # Create a list of suffix indices sorted by the suffixes they point to
return suffixes sorted_suffix_indices = sorted(range(n), key=lambda suffix_index: self.text[suffix_index:])
return sorted_suffix_indices
def build_lcp_array(self) -> List[int]: def build_lcp_array(self) -> List[int]:
""" """
Builds the LCP (Longest Common Prefix) array for the suffix array. Builds the LCP (Longest Common Prefix) array for the suffix array.
LCP[i] gives the length of the longest common prefix of the suffixes starting at suffix_array[i] and suffix_array[i-1]. LCP[i] gives the length of the longest common prefix of the suffixes
starting at suffix_array[i] and suffix_array[i-1].
Example: Example:
>>> sa = SuffixArray("banana") >>> sa = SuffixArray("banana")
@ -40,20 +42,18 @@ class SuffixArray:
lcp = [0] * n lcp = [0] * n
# Build the rank array where rank[i] gives the position of the suffix starting at index i # Build the rank array where rank[i] gives the position of the suffix starting at index i
for i, suffix in enumerate(suffix_array): for rank_index, suffix in enumerate(suffix_array):
rank[suffix] = i rank[suffix] = rank_index
h = 0 h = 0
for i in range(n): for i in range(n):
if rank[i] > 0: if rank[i] > 0:
j = suffix_array[rank[i] - 1] j = suffix_array[rank[i] - 1] # Previous suffix in the sorted order
while ( while (i + h < n) and (j + h < n) and self.text[i + h] == self.text[j + h]:
(i + h < n) and (j + h < n) and self.text[i + h] == self.text[j + h]
):
h += 1 h += 1
lcp[rank[i]] = h lcp[rank[i]] = h
if h > 0: if h > 0:
h -= 1 h -= 1 # Decrease h for the next suffix comparison
return lcp return lcp
def display(self) -> None: def display(self) -> None:
@ -71,26 +71,15 @@ class SuffixArray:
4: na 4: na
2: nana 2: nana
LCP Array:
LCP between a and ana: 1
LCP between ana and anana: 3
LCP between anana and banana: 0
LCP between banana and na: 0
LCP between na and nana: 2
""" """
print("Suffix Array:") print("Suffix Array:")
for idx in self.suffix_array: for suffix_index in self.suffix_array:
print(f"{idx}: {self.text[idx:]}") print(f"{suffix_index}: {self.text[suffix_index:]}")
print("\nLCP Array:")
for i in range(1, len(self.lcp_array)):
print(
f"LCP between {self.text[self.suffix_array[i - 1]:]} and {self.text[self.suffix_array[i]:]}: {self.lcp_array[i]}"
)
# Example usage: # Example usage:
if __name__ == "__main__": if __name__ == "__main__":
text = "banana" text = "banana"
sa = SuffixArray(text) sa = SuffixArray(text)
sa.display() sa.display() # Contribution for Hacktoberfest 2024