string names =
@"
王小强
张三
董强";
//使用了正则表达式的"零宽断言",可以参考这里:
//http://unibetter.com/deerchao/zhengzhe-biaodashi-jiaocheng-se.htm#lookaround
Regex re = new Regex(@"(?<=^\w)(?=\w$)", RegexOptions.Multiline);
string newNames = re.Replace(names, " ");
Console.WriteLine(newNames)
//results:
//王小强
//张 三
//董 强