int compareVersion(string version1, string version2) {

const int n1 = version1.length(), n2 = version2.length();

for (int i = 0, j = 0; i < n1 || j < n2; ++i, ++j) {

int v1 = 0, v2 = 0;

while (i < n1 && version1[i] != '.') {

v1 = v1 * 10 + version1[i++] - '0';

}

while (j < n2 && version2[j] != '.') {

v2 = v2 * 10 + version2[j++] - '0';

}

if (v1 != v2) {

return v1 > v2 ? 1 : -1;

}

}

return 0;

}