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:
1. 0.1 < 1.1 < 1.2 < 13.37

Solution:
1. public class Solution {
2. public int compareVersion(String version1, String version2) {
3. char[] c1 = version1.toCharArray();
4. char[] c2 = version2.toCharArray();
5. 6. int i = 0, j = 0, v1 = 0, v2 = 0, n1 = c1.length, n2 = c2.length;
7. 8. while (i < n1 && j < n2) {
9. // get version number v1 and v2
10. while (i < n1 && Character.isDigit(c1[i]))
11. v1 = v1 * 10 + c1[i++] - '0';
12. 13. while (j < n2 && Character.isDigit(c2[j]))
14. v2 = v2 * 10 + c2[j++] - '0';
15. 16. if (v1 > v2) return 1;
17. if (v2 > v1) return -1;
18. 19. // reset version numbers
20. v1 = 0; v2 = 0;
21. 22. // skip '.'
23. i++; j++;
24. }
25. 26. while (i < n1 && Character.isDigit(c1[i]))
27. v1 = v1 * 10 + c1[i++] - '0';
28. 29. while (j < n2 && Character.isDigit(c2[j]))
30. v2 = v2 * 10 + c2[j++] - '0';
31. 32. if (v1 > v2) return 1;
33. if (v1 < v2) return -1;
34. 35. return 0;
36. }
37. }