/// <summary>
/// 從字符串前面刪除指定字符個數
/// </summary>
/// <param name="s">字符串</param>
/// <param name="len">個數</param>
/// <returns>返回刪除后的字符串</returns>
public static string RemoveLeft(string s, int len)
{
    return s.PadLeft(len).Remove(0, len);
}

/// <summary>
/// 從字符串后面刪除指定字符個數
/// </summary>
/// <param name="s">字符串</param>
/// <param name="len">個數</param>
/// <returns>返回刪除后的字符串</returns>
public static string RemoveRight(string s, int len)
{
    s = s.PadRight(len);
    return s.Remove(s.Length - len, len);
}