Delete divide_and_conquer/Suffix Array and LCP implementation.py

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Putul Singh 2024-10-19 13:22:59 +05:30 committed by GitHub
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from typing import List
class SuffixArray:
def __init__(self, text: str) -> None:
"""
Initializes the class with the input text and builds the suffix and LCP arrays.
"""
self.text = text
self.suffix_array = self.build_suffix_array()
self.lcp_array = self.build_lcp_array()
def build_suffix_array(self) -> List[int]:
"""
Builds the suffix array for the input string.
Returns the suffix array (a list of starting indices of suffixes in sorted order).
Example:
>>> sa = SuffixArray("banana")
>>> sa.suffix_array
[5, 3, 1, 0, 4, 2]
"""
n = len(self.text)
# Create a list of suffix indices sorted by the suffixes they point to
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]:
"""
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].
Example:
>>> sa = SuffixArray("banana")
>>> sa.lcp_array
[0, 1, 3, 0, 0, 2]
"""
n = len(self.text)
suffix_array = self.suffix_array
rank = [0] * n
lcp = [0] * n
# Build the rank array where rank[i] gives the position of the suffix starting at index i
for rank_index, suffix in enumerate(suffix_array):
rank[suffix] = rank_index
h = 0
for i in range(n):
if rank[i] > 0:
j = suffix_array[rank[i] - 1] # Previous suffix in the sorted order
while (
(i + h < n) and (j + h < n) and self.text[i + h] == self.text[j + h]
):
h += 1
lcp[rank[i]] = h
if h > 0:
h -= 1 # Decrease h for the next suffix comparison
return lcp
def display(self) -> None:
"""
Displays the suffix array and LCP array for the input string.
Example:
>>> sa = SuffixArray("banana")
>>> sa.display()
Suffix Array:
5: a
3: ana
1: anana
0: banana
4: na
2: nana
"""
print("Suffix Array:")
for suffix_index in self.suffix_array:
print(f"{suffix_index}: {self.text[suffix_index:]}")
# Example usage:
if __name__ == "__main__":
text = "banana"
sa = SuffixArray(text)
sa.display() # Contribution for Hacktoberfest 2024