Reverse String

#include<iostream>
using namespace std;

// Recursive function to reverse a string
void reverse(string& str, int i, int j ) {

    // Printing the current state of the string in each recursive call
    cout << "call received for " << str << endl;

    // Base case: If left index crosses right index, stop recursion
    if(i > j)
        return;

    // Swap characters at i-th and j-th position
    swap(str[i], str[j]);

    // Move indices closer towards the center
    i++;
    j--;

    // Recursive call to continue swapping the next pair
    reverse(str, i, j);
}

int main() {
    string name = "abcde"; // Example input
    cout << endl;

    // Call reverse function with the entire string
    reverse(name, 0, name.length()-1);

    cout << endl;

    // Print the reversed string
    cout << name << endl;

    return 0;
}

Example Walkthrough:

Let’s take an example string “abcde” and analyze how the recursive function works.

1. Initial Call: reverse("abcde", 0, 4)

   • i = 0, j = 4
   • Swap str[0] = 'a' and str[4] = 'e'
   • String becomes "ebcda"
   • Recursive Call: reverse("ebcda", 1, 3)

2. Second Call: reverse("ebcda", 1, 3)

   • i = 1, j = 3
   • Swap str[1] = 'b' and str[3] = 'd'
   • String becomes "edcba"
   • Recursive Call: reverse("edcba", 2, 2)

3.Third Call: reverse("edcba", 2, 2)

• i = 2, j = 2 (same index)
• No swap needed, recursion stops here.
• Function returns to the previous calls.

4. Returning back through recursion stack

   • Since all calls return, the final reversed string is "edcba".