public class Solution { public string DefangIPaddr(string address) { var list = address.ToList( ); for(int i = 0; i < list.Count; i++) { if(list[i] == '.') { list.Insert( i , '[' ); i += 1; list.Insert( i + 1, ']' ); i += 1; } } string result = new string( list.ToArray( ) ); return result; } }