template <class T> unsigned int edit_distance(const T& s1, const T& s2)
{
const size_t len1 = s1.size(), len2 = s2.size();
vector<vector<unsigned int> > d(len1 + 1, vector<unsigned int>(len2 + 1));
d[0][0] = 0;
for(unsigned int i = 1; i <= len1; ++i) d[i][0] = i;
for(unsigned int i = 1; i <= len2; ++i) d[0][i] = i;
for(unsigned int i = 1; i <= len1; ++i){
for(unsigned int j = 1; j <= len2; ++j){
d[i][j] = std::min( std::min(d[i - 1][j] + 1,d[i][j - 1] + 1), d[i - 1][j - 1] + (s1[i - 1] == s2[j - 1] ? 0 : 1) );
}
}
return d[len1][len2];
}

SOURCE