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();
  6.     int i = 0, j = 0, v1 = 0, v2 = 0, n1 = c1.length, n2 = c2.length;
  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';
  13.       while (j < n2 && Character.isDigit(c2[j])) 
  14.         v2 = v2 * 10 + c2[j++] - '0';
  16.       if (v1 > v2) return 1;
  17.       if (v2 > v1) return -1;
  19.       // reset version numbers
  20.       v1 = 0; v2 = 0;
  22.       // skip '.'
  23.       i++; j++;
  24.     }
  26.     while (i < n1 && Character.isDigit(c1[i])) 
  27.       v1 = v1 * 10 + c1[i++] - '0';
  29.     while (j < n2 && Character.isDigit(c2[j])) 
  30.       v2 = v2 * 10 + c2[j++] - '0';
  32.     if (v1 > v2) return 1;
  33.     if (v1 < v2) return -1;
  35.     return 0;
  36.   }
  37. }