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 s1 using only one call to isSubstring (i.e., “waterbottle” is a rotation of “erbottlewat”).

#include <iostream>
using namespace std;

bool isSubstring(string s1, string s2)
{
    /*
        string::find
        The position of the first character of the first match.
        If no matches were found, the function returns string::npos.
     */
    if(s1.find(s2) != s1.npos)
        return true;
    else
        return false;
}
bool isRotation(string s1, string s2)
{
    if( (s1.length() == s2.length()) && s1.length() > 0)
        return isSubstring(s1+s1, s2);
    else
        return false;
}

int main(int argc, const char * argv[])
{
    string s1 = "abcdef";
    string s2 = "cdefab";
    if(isRotation(s1,s2))
        cout<<"TRUE"<<endl;
    else
        cout<<"FALSE"<<endl;
    
    return 0;
}