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edit_distance.py
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edit_distance.py
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__author__ = 'tg'
from util.arrays import format_2d_array
import sys
def min_lavenshtein_distance(s1, s2):
'''
Computes Minimum Lavenshtein Distance between two strings
:param s1: string 1
:param s2: string 2
:return: minimum edit distance
'''
s1 = '#' + s1 # An empty space is added to make space for base case
s2 = '#' + s2 # An empty space is added to make space for base case
n = len(s1)
m = len(s2)
# declaring an empty array
matrix = [[0 for i in range(m)] for i in range(n)]
for i in range(n):
for j in range(m):
if i == 0: # base case 1
distance = j
elif j == 0: # base case 2
distance = i
else: # general case
distance = sys.maxint # use this as reference to find minimum distance
if matrix[i-1][j] + 1 < distance: #horizontal move, insert s2 char
distance = matrix[i-1][j] + 1
if matrix[i][j-1] + 1 < distance: #vertical move, insert a char from s1
distance = matrix[i][j-1] + 1
# diagonal move :
# the distance increases if the characters are different (substitution)
# the distance remains same if characters are same
diagonal_dist = matrix[i-1][j-1] + (0 if s1[i] == s2[j] else 2)
if diagonal_dist < distance:
distance = diagonal_dist
matrix[i][j] = distance
print format_2d_array(matrix, s1, s2)
return matrix[n-1][m-1]
if __name__ == '__main__':
s1 = 'intention'
s2 = 'execution'
min_edit_distance = min_lavenshtein_distance(s1, s2)
print min_edit_distance