165. 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.

You may assume the default revision number for each level of a version number to be 0. For example, version number 3.4 has a revision number of 3 and 4 for its first and second level revision number. Its third and fourth level revision number are both 0.

Example 1:

Input: version1 = "0.1", version2 = "1.1"
Output: -1

Example 2:

Input: version1 = "1.0.1", version2 = "1"
Output: 1

Example 3:

Input: version1 = "7.5.2.4", version2 = "7.5.3"
Output: -1

Example 4:

Input: version1 = "1.01", version2 = "1.001"
Output: 0
Explanation: Ignoring leading zeroes, both “01” and “001" represent the same number “1”

Example 5:

Input: version1 = "1.0", version2 = "1.0.0"
Output: 0
Explanation: The first version number does not have a third level revision number, which means its third level revision number is default to "0"

class Solution {
    public int compareVersion(String version1, String version2) {
        int i = 0, j = 0;
        int l1 = version1.length(), l2 = version2.length();
        
        while(i < l1 || j < l2){
            int c1 = 0, c2 = 0;
            while(i < l1 && version1.charAt(i) != '.'){
                c1 = c1 * 10 + version1.charAt(i) - '0';
                i++;
            }
            i++;
            while(j < l2 && version2.charAt(j) != '.'){
                c2 = c2 * 10 + version2.charAt(j) - '0';
                j++;
            }
            j++;
            if(c1 > c2) return 1;
            if(c1 < c2) return -1;
        }
        return 0;
    }
}

以dot为区分，每次比较dot中间的数值，因为每次比较前都会重新置零，所以如果有leading zero就可以自动排除。每次计算完后比较大小，否则最后返回0.