CompareVersionNumbers.java

/*
Compare two version numbers version1 and version2.
If version1 > version2 return 1, if version1 < version2 return -1, otherwise return 0.

You may assume that the version strings are non-empty and contain only digits and the . character.
The . character does not represent a decimal point and is used to separate number sequences.
For instance, 2.5 is not "two and a half" or "half way to version three", it is the fifth second-level revision of the second first-level revision.

Here is an example of version numbers ordering:

0.1 < 1.1 < 1.2 < 13.37

*/
import java.util.*;

public class CompareVersionNumbers {
	public static int compareVersion(String version1, String version2) {
        if(version1.length() <= 0 || version2.length() <= 0) return 0;
        int L1 = version1.length();
        int L2 = version2.length();
        int i = 0;
        int j = 0;
        while(i < L1 || j < L2){
            int v1 = 0;
            int v2 = 0;
            while( i < L1 && version1.charAt(i) != '.'){
                v1 = v1*10 + version1.charAt(i) - '0';
                i++;
            }
            while(j < L2 && version2.charAt(j) != '.'){
                v2 = v2*10 + version2.charAt(j) - '0';
                j++;
            }
            
            if(v1 < v2){
                return -1;
            }else if(v1 > v2){
                return 1;
            }else{
                i++;
                j++;
            }
        }
        return 0;
        
    }	

	public static void main(String[] args) {
		String  s = "12.152";
		String t = "12.22";
		int res = compareVersion(s, t);
		System.out.println("String 1: " + s);
		System.out.println("String 2: " + t);
		System.out.println("Resulte: " + res);
		return;
	}	
}