Write a Windows form application that returns the difference of two given files using Levenshtein distance (edit distance).
A commonly-used bottom-up dynamic programming algorithm for computing the Levenshtein distance involves the use of an (n + 1) × (m + 1) matrix, where n and m are the lengths of the two strings. Here is pseudocode for a function LevenshteinDistance that takes two strings, s of length m, and t of length n, and computes the Levenshtein distance between them:
int LevenshteinDistance(char s[1..m], char t[1..n])
// d is a table with m+1 rows and n+1 columns
declare int d[0..m, 0..n]
for i from 0 to m
d[i, 0] := i
for j from 1 to n
d[0, j] := j
for i from 1 to m
for j from 1 to n
if s[i] = t[j] then cost := 0
else cost := 1
d[i, j] := minimum(
d[i-1, j] + 1, // deletion
d[i, j-1] + 1, // insertion
d[i-1, j-1] + cost // substitution
)
return d[m, n]
Two examples of the resulting matrix (the minimum steps to be taken are highlighted):
k i t t e n
0 1 2 3 4 5 6
s 1 1 2 3 4 5 6
i 2 2 1 2 3 4 5
t 3 3 2 1 2 3 4
t 4 4 3 2 1 2 3
i 5 5 4 3 2 2 3
n 6 6 5 4 3 3 2
g 7 7 6 5 4 4 3
S a t u r d a y
0 1 2 3 4 5 6 7 8
S 1 0 1 2 3 4 5 6 7
u 2 1 1 2 2 3 4 5 6
n 3 2 2 2 3 3 4 5 6
d 4 3 3 3 3 4 3 4 5
a 5 4 3 4 4 4 4 3 4
y 6 5 4 4 5 5 5 4 3
The invariant maintained throughout the algorithm is that we can transform the initial segment s[1..i] into t[1..j] using a minimum of d[i,j] operations. At the end, the bottom-right element of the array contains the answer.