24 lines
761 B
Python
24 lines
761 B
Python
def lcs(a, b):
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lengths = [[0 for j in range(len(b)+1)] for i in range(len(a)+1)]
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# row 0 and column 0 are initialized to 0 already
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for i, x in enumerate(a):
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for j, y in enumerate(b):
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if x == y:
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lengths[i+1][j+1] = lengths[i][j] + 1
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else:
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lengths[i+1][j+1] = max(lengths[i+1][j], lengths[i][j+1])
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# read the substring out from the matrix
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result = ""
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x, y = len(a), len(b)
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while x != 0 and y != 0:
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if lengths[x][y] == lengths[x-1][y]:
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x -= 1
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elif lengths[x][y] == lengths[x][y-1]:
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y -= 1
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else:
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assert a[x-1] == b[y-1]
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result = a[x-1] + result
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x -= 1
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y -= 1
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return result
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