class Solution {
public:
    int compareVersion(string version1, string version2) {
        int sz1 = version1.size(), sz2 = version2.size(), i1 = 0, i2 = 0, sum1, sum2;
        while (i1 < sz1 || i2 < sz2)
        {
            sum1 = sum2 = 0;
            while (i1 < sz1 && version1[i1] != '.')
            {
                sum1 *= 10;
                sum1 += version1[i1] - '0';
                ++i1;
            }

            while (i2 < sz2 && version2[i2] != '.')
            {
                sum2 *= 10;
                sum2 += version2[i2] - '0';
                ++i2;
            }
            if (sum1 > sum2)
                return 1;
            if (sum2 > sum1)
                return -1;
            if (i1 < sz1)
                ++i1;
            if (i2 < sz2)
                ++i2;
        }
        return 0;
    }
};