54 lines
1.5 KiB
Python
54 lines
1.5 KiB
Python
''' mbinary
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#########################################################################
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# File : lcs.py
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# Author: mbinary
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# Mail: zhuheqin1@gmail.com
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# Blog: https://mbinary.xyz
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# Github: https://github.com/mbinary
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# Created Time: 2018-08-25 12:00
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# Description:
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#########################################################################
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'''
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def lcs(a, b):
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'''time: O(mn); space: O(mn)'''
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m, n = len(a), len(b)
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board = [[[] for i in range(n+1)] for i in range(m+1)]
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for i in range(m):
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for j in range(n):
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if a[i] == b[j]:
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board[i+1][j+1] = board[i][j]+[a[i]]
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elif len(board[i][j+1]) < len(board[i+1][j]):
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board[i+1][j+1] = board[i+1][j]
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else:
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board[i+1][j+1] = board[i][1+j]
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return board[m][n]
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def lcs2(a, b):
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'''time: O(mn); space: O(m)'''
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m, n = len(a), len(b)
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board = [[] for i in range(n+1)]
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for i in range(m):
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upperLevel = board[0].copy()
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for j in range(n):
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tmp = board[j+1].copy()
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if a[i] == b[j]:
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board[j+1] = upperLevel+[a[i]]
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elif len(board[j+1]) < len(board[j]):
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board[j+1] = board[j].copy() # copy is needed
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upperLevel = tmp
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return board[n]
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if __name__ == '__main__':
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a = 'ABCBDAB'
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b = 'BDCABA'
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print('s1:', a)
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print('s2:', b)
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while 1:
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print('lcs:', lcs2(a, b))
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a = input('s1: ')
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b = input('s2: ')
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