python-string-similarity/strsim/longest_common_subsequence.py

# Copyright (c) 2018 luozhouyang
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
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# furnished to do so, subject to the following conditions:
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# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
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# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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import numpy as np

from .string_distance import StringDistance


class LongestCommonSubsequence(StringDistance):
    def distance(self, s0, s1):
        if s0 is None:
            raise TypeError("Argument s0 is NoneType.")
        if s1 is None:
            raise TypeError("Argument s1 is NoneType.")
        if s0 == s1:
            return 0.0
        return len(s0) + len(s1) - 2 * self.length(s0, s1)

    @staticmethod
    def length(s0, s1):
        if s0 is None:
            raise TypeError("Argument s0 is NoneType.")
        if s1 is None:
            raise TypeError("Argument s1 is NoneType.")
        s0_len, s1_len = len(s0), len(s1)
        x, y = s0[:], s1[:]
        n, m = s0_len + 1, s1_len + 1
        matrix = np.zeros((n, m))
        for i in range(1, s0_len + 1):
            for j in range(1, s1_len + 1):
                if x[i - 1] == y[j - 1]:
                    matrix[i][j] = matrix[i - 1][j - 1] + 1
                else:
                    matrix[i][j] = max(matrix[i][j - 1], matrix[i - 1][j])
        return matrix[s0_len][s1_len]