Compare Version Numbers

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


这题还是蛮有意思的，就是版本号之间的比较，刚开始没考虑到例如1.6.5与1.6之间的比较，没有想到用递归的方法，解决起来就比较困难了。。

public class Solution {
    public int compareVersion(String version1, String version2) {
        
        if(version1.equals(version2)){
            return 0;
        }
        
        int first1,first2;
        String second1,second2;
        if(version1.contains(".")){
            String[] str=version1.split("\.",2);
            first1=Integer.parseInt(str[0]);
            second1=str[1];
        }
        else{
            first1=Integer.parseInt(version1);
            second1="0";
        }
        
        if(version2.contains(".")){
            String[] str=version2.split("\.",2);
            first2=Integer.parseInt(str[0]);
            second2=str[1];
        }
        else{
            first2=Integer.parseInt(version2);
            second2="0";
        }
        
        
        if(first1>first2){
            return 1;
        }
        else if(first1<first2){
            return -1;
        }
        
        else return compareVersion(second1,second2);
    }
}