LINQ method for Edit Operations (inser, delet subst) using Levenshtein algo.

LevenshteinExtension.cs

//Levenshtein distance.  ->.  "HolA".EditDifferences("Hola").Count()

//Optimal edit operations ->.  "HolA".EditDifferences("Hola").Reverse()
// returns  the list of operations as a 2-tuple (op_string, item)
// where op_string is "+" for insert, "-" deletions and "~" substitution

public static  IEnumerable<(string, TSource)> EditDifferences<TSource>(this IEnumerable<TSource> input, IEnumerable<TSource> old){
    TSource[] s1 = input.ToArray(), s2 = old.ToArray(); //cache for random access
    int[,] matrix = new int[s1.Count()+1, s2.Count()+1];
    
    //Levenshtein matrix
    for (int i = 0; i <= s1.Count(); i++) {
        for (int j = 0; j <= s2.Count(); j++) {
            if (Math.Min(i, j) == 0) matrix[i,j] = Math.Max(i, j);
            else
                matrix[i,j] = new[] {
                            matrix[i-1, j] + 1,
                            matrix[i, j-1] + 1,
                            matrix[i-1, j-1] + (s1[i-1].Equals(s2[j-1]) ? 0 : 1)
                }.Min();
        }
    }

    // Backtracking (non w.)
    int ii = input.Count(), jj = old.Count();
    while (ii >= 1 && jj >=1){
        if (matrix[ii-1,jj-1] < matrix[ii,jj]){
            ii--; jj--;
            yield return ("~"+s2[jj], s1[ii] ); 
        } else if (matrix[ii,jj-1] < matrix[ii,jj]){
            jj--;
            yield return ("+", s2[jj]);
        } else if (matrix[ii-1,jj] < matrix[ii,jj]){
            ii--;
            yield return ("-", s1[ii]);
        } else if (matrix[ii,jj] == matrix[ii,jj]){
            ii--; jj--;
        } else {break;}
    }
}