1.8 Assume you have a method isSubstring which checks if one word is a substring of another. Given two strings, s1 and s2, write code to check if s2 is a rotation of si using only one call to isSubstring (e.g.,"waterbottle"is a rota- tion of"erbottlewat").

1.8.cpp

#include<iostream>

using namespace std;

bool isSubstring(const string &s1, const string &s2)
{
    return s1.find(s2) != string::npos;
}

bool isRotation(const string &s1, const string &s2)
{
    if (s1.size() == s2.size() && s1.size() > 0) {
        string s1s1 = s1 + s1;
        return isSubstring(s1s1, s2);
    }
    return false;
}

int main(int argc, char *argv[])
{
    cout << isRotation("waterbottle", "terbottlewa") << endl;
    return 0;
}