Python/dynamic_programming/edit_distance.py
Sanders Lin 7a6ebb85a2 Update edit_distance.py (#1001)
added bottom up method.
2019-07-13 09:10:02 +02:00

110 lines
3.0 KiB
Python

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