class LCS(DP):
"""
Counting and calculate the longest common string algorithm.
The problem's description is as below.
http://www.geeksforgeeks.org/dynamic-programming-set-4-longest-common-subsequence/
"""
def __init__(self, str1=None, str2=None):
self._suffix_matrix = SuffixMatrix(str1, str2)
self._matrix = self._suffix_matrix.suffix_matrix
self._str1 = str1
self._str2 = str2
self._lcs = []
def _algorithm(self):
"""
LCS algorithm.
"""
for i, s in enumerate(self._str2):
for j, t in enumerate(self._str1):
if t == s:
self._matrix[i + 1][j + 1]['len'] = self._matrix[i][j].get('len') + 1
self._matrix[i + 1][j + 1]['direct'] = 'ul'
else:
self._matrix[i + 1][j + 1]['len'] = \
max(self._matrix[i + 1][j].get('len'), self._matrix[i][j + 1].get('len'))
self._matrix[i + 1][j + 1]['direct'] = \
'l' if self._matrix[i + 1][j].get('len') >= self._matrix[i][j + 1].get('len') else 'u'
def _backtracking(self):
"""
using backtracking to find the lcs.
"""
def inner_backtracking(i, j):
{
'ul': lambda: (inner_backtracking(i - 1, j - 1),
self._lcs.append(self._str1[j - 1])),
'u': lambda: inner_backtracking(i - 1, j),
'l': lambda: inner_backtracking(i, j - 1)
}.get(self._matrix[i][j]['direct'], lambda: None)()
inner_backtracking(len(self._str2), len(self._str1))
def res(self):
"""
running the lcs algorithm and backtracking for getting the result.
:return: (lcs length, lcs string)
"""
self._algorithm()
self._backtracking()
return self._matrix[len(self._str2)][len(self._str1)].get('len'), ''.join(self._lcs)
def show_matrix(self):
self._suffix_matrix.show_suffix()
def __init__(self, str1=None, str2=None):
self._suffix_matrix = SuffixMatrix(str1, str2)
self._matrix = self._suffix_matrix.suffix_matrix
self._str1 = str1
self._str2 = str2
self._lcs = []
