#include <string>
#include <iostream>
using namespace std;
 
string reverse_helper(string& s,int length,int start=0){
 
    if (start>=length){
        return s;
    }
    else{
        char temp=s[length];
        s[length]=s[start];
        s[start]=temp;
        reverse_helper(s,--length,++start);
    }return s;
}
 
string reverse(string str, int length, int start=0)
{
    return reverse_helper(str, length, start);
}
 
int main(void) {
 
    string a = "This is a long string";
    cout<<reverse(a,a.length()-1,0) << "\n";
    cout << "original string: " << a;
}

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