string rec_rev_str(string *str,int size){
if(size == 0){
return *str;
}
swap((*str)[0],(*str)[size]);`// size is the index from the end`


return rec_rev_str(str 1,size-1);
}

int main(){
  string str = "great";
  int size = 5;
  int start = 0;
  int end = size - 1;
  string* ptr = &str;  
  
  rec_rev_str(ptr,size-1);

  cout<<str<<endl;
}

1. I don't understand how to point str 1 (the first index of the string like we do in an array e.g. arr 1)

CodePudding user response：

#include <iostream>
#include <string>
#include <algorithm>

// pass string by reference so we can swap in place
void reverse(std::string& input, size_t leftIndex, size_t rightIndex){
    if(leftIndex < rightIndex){  
        // <algorithm> header has a swap implementation
        std::swap(input[leftIndex], input[rightIndex]);
        // increment index from left, decrement from right, and continue swapping
        reverse(input, leftIndex 1, rightIndex-1);
    }
}

int main() {
    std::string inputString = "Hello, world!";
    reverse(inputString, 0, inputString.size() - 1);
    std::cout << inputString << std::endl;
    return 0;
}

CodePudding user response：

string is not an array. If you see str 1 it means that wants to read the 'next string' so if you had an array of strings and a pointer str pointing into the array (to a string) str 1 was the pointer to the next element of the array. If you want to handle the caracters of a string with pointers you can do so with the c_str() method of the string

void rec_rev_str_rec(char *str,int size){
    if(size == 0){
        return ;
    }
    swap(str[0],str[size]);
    rec_rev_str_rec(str 1,size-2);//-2 because the first and the last elemenst are swapped
}

string rec_rev_str(string* s,int size){
    rec_rev_str_rec(s->c_str(),size);
    return s;
}
//or
string rec_rev_str2(string& s,int size){
    rec_rev_str_rec(s.c_str(),size);
    return s;
}