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110 lines
3.0 KiB
Python
110 lines
3.0 KiB
Python
"""
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Author : Turfa Auliarachman
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Date : October 12, 2016
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This is a pure Python implementation of Dynamic Programming solution to the edit distance problem.
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The problem is :
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Given two strings A and B. Find the minimum number of operations to string B such that A = B. The permitted operations are removal, insertion, and substitution.
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"""
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from __future__ import print_function
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class EditDistance:
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"""
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Use :
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solver = EditDistance()
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editDistanceResult = solver.solve(firstString, secondString)
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"""
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def __init__(self):
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self.__prepare__()
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def __prepare__(self, N = 0, M = 0):
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self.dp = [[-1 for y in range(0,M)] for x in range(0,N)]
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def __solveDP(self, x, y):
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if (x==-1):
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return y+1
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elif (y==-1):
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return x+1
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elif (self.dp[x][y]>-1):
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return self.dp[x][y]
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else:
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if (self.A[x]==self.B[y]):
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self.dp[x][y] = self.__solveDP(x-1,y-1)
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else:
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self.dp[x][y] = 1+min(self.__solveDP(x,y-1), self.__solveDP(x-1,y), self.__solveDP(x-1,y-1))
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return self.dp[x][y]
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def solve(self, A, B):
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if isinstance(A,bytes):
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A = A.decode('ascii')
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if isinstance(B,bytes):
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B = B.decode('ascii')
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self.A = str(A)
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self.B = str(B)
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self.__prepare__(len(A), len(B))
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return self.__solveDP(len(A)-1, len(B)-1)
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def min_distance_bottom_up(word1: str, word2: str) -> int:
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"""
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>>> min_distance_bottom_up("intention", "execution")
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5
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>>> min_distance_bottom_up("intention", "")
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9
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>>> min_distance_bottom_up("", "")
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0
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"""
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m = len(word1)
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n = len(word2)
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dp = [[0 for _ in range(n+1) ] for _ in range(m+1)]
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for i in range(m+1):
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for j in range(n+1):
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if i == 0: #first string is empty
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dp[i][j] = j
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elif j == 0: #second string is empty
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dp[i][j] = i
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elif word1[i-1] == word2[j-1]: #last character of both substing is equal
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dp[i][j] = dp[i-1][j-1]
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else:
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insert = dp[i][j-1]
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delete = dp[i-1][j]
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replace = dp[i-1][j-1]
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dp[i][j] = 1 + min(insert, delete, replace)
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return dp[m][n]
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if __name__ == '__main__':
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try:
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raw_input # Python 2
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except NameError:
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raw_input = input # Python 3
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solver = EditDistance()
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print("****************** Testing Edit Distance DP Algorithm ******************")
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print()
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print("Enter the first string: ", end="")
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S1 = raw_input().strip()
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print("Enter the second string: ", end="")
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S2 = raw_input().strip()
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print()
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print("The minimum Edit Distance is: %d" % (solver.solve(S1, S2)))
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print("The minimum Edit Distance is: %d" % (min_distance_bottom_up(S1, S2)))
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print()
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print("*************** End of Testing Edit Distance DP Algorithm ***************")
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