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

public class Solution {
    public int compareVersion(String version1, String version2) {
        int len1 = version1.length();
        int len2 = version2.length();
        int i = 0;
        int j = 0;
        int a = 0;
        int b = 0;
        while (i < len1 || j < len2) {
        	while (i < len1 && version1.charAt(i) != '.') {
        		a = a * 10 + (version1.charAt(i) - '0');
        		i++;
        	}
        	while (j < len2 && version2.charAt(j) != '.') {
        		b = b * 10 + (version2.charAt(j) - '0');
        		j++;
        	}
        	if (a > b) {
        		return 1;
        	} else if (a < b) {
        		return -1;
        	}
        	i++;
        	j++;
        	a = b = 0;
        }
        return 0;
    }
}