pattern = "((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)";

String from0to199="[0-1]?\d{1,2}"; String from200to249="2[0-4]?\d"; String from250to255="25[0-5]"; String from0to255 ="(" + from0to199 + "|" + from200to249 + "|" + from250to255 + ")"; String dot="\."; String pattern=from0to255+dot+from0to255+dot+from0to255+dot+from0to255;

Seriously, Is this a Java exercice?!

finally I did it Because of Zeros at the beginig i waste so much time. import java.io.; import java.util.; import java.util.regex.*;

public class Solution {

public static void main(String[] args) {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */


    Scanner sc = new Scanner(System.in);

    while (sc.hasNext()) {
        String str = sc.next();
        System.out.println(isValidIP(str));
    }


}

public static  boolean isValidIP (String str) {
     MyRegex myRegex = new MyRegex();


    return str.matches(myRegex.strPatern);

}

}

class MyRegex { public String strPatern = "^(0{0,2}[0-9]|0[0-9]{2}|[0-9]{1,2}|1[0-9]{2}|2[0-4][0-9]|25[0-5])\." + "(0{0,2}[0-9]|0[0-9]{2}|[0-9]{1,2}|1[0-9]{2}|2[0-4][0-9]|25[0-5])\." + "(0{0,2}[0-9]|0[0-9]{2}|[0-9]{1,2}|1[0-9]{2}|2[0-4][0-9]|25[0-5])\." + "(0{0,2}[0-9]|0[0-9]{2}|[0-9]{1,2}|1[0-9]{2}|2[0-4][0-9]|25[0-5])$";

public MyRegex() {}

}

This is a great exercise for understanding how to construct complex regular expressions! cricketbuzz mahadev