namespace WebApp; public static class Helper { public static string ToLetters(int number) { var result = ""; while (number > 0) { number--; // Adjust for 1-based indexing char letter = (char)('A' + (number % 26)); result = letter + result; number /= 26; } return result; } public static (int Row, int Col) ToRowCol(string letters) { int row = 0; int col = 0; foreach (var item in letters) { if (item >= 'A') { row = row * 26 + (item - 'A' + 1); } else if (item >= '0') { col = col * 10 + (item - '0'); } } return (row, col); } }