今天面试有一道面试题没解出来，郁闷啊

Question

唉。首先，你应该看到这样的3部分  123<em>abc       456<em>def       789。这三部分是用 </em> 分割的。剩下的一步，你自己想吧。

Answer 1

        static string GetString(string source, int len)
        {
            string newSource = source.Replace("<em>", "");
            newSource = newSource.Replace("</em>", "");
            if (newSource.Length < len)
            {
                throw new Exception("要截取的长度超出了限制");
            }
            int lastIndex = source.LastIndexOf("</em>");
            string endValue = lastIndex < source.Length - 5 ? source.Substring(lastIndex + 5, source.Length - lastIndex - 5) : "";            StringBuilder sb = new StringBuilder();
            MatchCollection maths = Regex.Matches(source, "(?<value>[^>]*)(?<em>[<][/]?em[>])");            for (int i = 0; i < maths.Count; i++)
            {
                string value = maths[i].Groups["value"].Value;
                string em = maths[i].Groups["em"].Value;
                if (value.Length <= len)
                {
                    if (em == "</em>")
                    {
                        sb.AppendFormat("<em>{0}</em>", value);
                    }
                    else
                    {
                        sb.Append(value);
                    }
                    len -= value.Length;
                }
                else
                {
                    sb.Append(value.Substring(0, len));
                    len -= value.Length;
                    break;
                }
            }
            if (len > 0)
            {
                sb.Append(endValue.Substring(0, len));
            }            return sb.ToString();
        }坐等更好的办法

Answer 2

正则写错了 改为(?<value>[^<]*)(?<em>[<][/]?em[>])