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 自己写的代码跟discuss的最优代码几乎相同，不知道还有没有优化空间

int compareVersion(string version1, string version2) {    int i = 0, j = 0;    while (i < version1.length() || j < version2.length())    {        int a1 = 0;        int a2 = 0;                while (i < version1.length() && version1[i] != '.')            a1 = a1 * 10 + version1[i++] - '0';        while (j < version2.length() && version2[j] != '.')            a2 = a2 * 10 + version2[j++] - '0';        i++; j++;        if (a1 > a2)            return 1;        else if (a1 < a2)            return -1;    }    return 0;}