Program to reverse a string (Iterative and Recursive)

Given a string, write a recursive program to reverse it.

string-reverse

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Method 1 (Using Stack)

C++

// C++ program to reverse a string using stack 
#include <bits/stdc++.h> 
using namespace std; 
  
void recursiveReverse(string &str) 
{ 
   stack<char> st; 
   for (int i=0; i<str.length(); i++) 
       st.push(str[i]); 
  
   for (int i=0; i<str.length(); i++) { 
       str[i] = st.top(); 
       st.pop(); 
   }        
} 
  
// Driver program 
int main() 
{ 
    string str = "geeksforgeeks"; 
    recursiveReverse(str); 
    cout << str; 
    return 0; 
} 

Java

// Java program to reverse a string using stack 
import java.util.*; 
class GFG 
{ 
  public static String recursiveReverse(char []str)  
 {  
   Stack<Character> st = new Stack<>();  
   for(int i=0; i<str.length; i++)  
        st.push(str[i]);  
  
   for (int i=0; i<str.length; i++) {  
    str[i] = st.peek();  
    st.pop();  
   }      
   return String.valueOf(str);// converting character array to string 
 }  
  
// Driver program  
   public static void main(String []args)  
   {  
      String str = "geeksforgeeks";  
      str = recursiveReverse(str.toCharArray());// passing character array as parameter  
      System.out.println(str);  
   } 
} 
// This code is contributed by Adarsh_Verma 

Python3

# Python program to reverse a string using stack 
  
def recursiveReverse(str): 
      
    # using as stack 
    stack = [] 
  
    for i in range(len(str)): 
        stack.append(str[i]) 
      
    for i in range(len(str)): 
        str[i] = stack.pop() 
  
if __name__ == "__main__": 
    str = "geeksforgeeks"
  
    # converting string to list 
    # because strings do not support 
    # item assignment 
    str = list(str) 
    recursiveReverse(str) 
  
    # converting list to string 
    str = ''.join(str) 
    print(str) 
      
# This code is contributed by 
# sanjeev2552 

C#

// C# program to reverse a string using stack  
using System; 
using System.Collections.Generic; 
  
class GFG  
{  
    public static String recursiveReverse(char []str)  
    {  
        Stack<char> st = new Stack<char>();  
        for(int i = 0; i < str.Length; i++)  
            st.Push(str[i]);  
  
        for (int i = 0; i < str.Length; i++)  
        {  
            str[i] = st.Peek();  
            st.Pop();  
        }  
          
        // converting character array to string 
        return String.Join("",str);  
    }  
  
    // Driver program  
    public static void Main()  
    {  
        String str = "geeksforgeeks";  
          
        // passing character array as parameter 
        str = recursiveReverse(str.ToCharArray());  
        Console.WriteLine(str);  
    }  
}  
  
// This code is contributed by Rajput-Ji 

Output:

skeegrofskeeg

Time complexity : O(n)
Auxiliary Space : O(n)

Method 2 (Iterative)

C++

// A Simple Iterative C++ program to reverse 
// a string 
#include <bits/stdc++.h> 
using namespace std; 
  
// Function to reverse a string 
void reverseStr(string& str) 
{ 
    int n = str.length(); 
  
    // Swap character starting from two 
    // corners 
    for (int i = 0; i < n / 2; i++) 
        swap(str[i], str[n - i - 1]); 
} 
  
// Driver program 
int main() 
{ 
    string str = "geeksforgeeks"; 
    reverseStr(str); 
    cout << str; 
    return 0; 
} 

Java

// A Simple Java program  
// to reverse a string 
import java.util.Scanner; 
  
public class reverseStr 
{ 
// Function to reverse  
// a string 
void stringReverse() 
{ 
    String str = "geeksforgeeks"; 
    int length = str.length(); 
    StringBuffer revString = new StringBuffer(); 
    for (int i = length - 1;  
             i >= 0; i--)  
    { 
        revString.append(str.charAt(i)); 
    } 
    System.out.println(revString); 
} 
  
// Driver Code 
public static void main(String []args) 
{ 
    reverseStr s= new reverseStr(); 
    s.stringReverse(); 
} 
} 
  
// This code is contributed  
// by prabhat kumar singh  

Python

# A Simple python program  
# to reverse a string 
  
# Function to 
# reverse a string 
def reverseStr(str): 
    n = len(str) 
      
    # initialising a empty 
    # string 'str1' 
    str1 = '' 
    i = n - 1
    while i >= 0: 
          
        # copy str  
        # to str1 
        str1 += str[i] 
        i -= 1
    print(str1)      
  
# Driver Code  
def main(): 
    str = "geeksforgeeks"; 
    reverseStr(str); 
      
if __name__=="__main__": 
    main()      
      
# This code is contributed  
# by prabhat kumar singh  

C#

// A Simple Iterative C# program to reverse 
// a string 
using System; 
  
class GFG 
{ 
  
// Function to reverse a string 
static String reverseStr(String str) 
{ 
    int n = str.Length; 
  
    // Swap character starting from two 
    // corners 
    for (int i = 0; i < n / 2; i++) 
        str = swap(str,i,n - i - 1); 
    return str; 
} 
static String swap(String str, int i, int j)  
{  
    char []ch = str.ToCharArray();  
    char temp = ch[i];  
    ch[i] = ch[j];  
    ch[j] = temp;  
    return String.Join("",ch);  
} 
  
// Driver code 
public static void Main(String[] args) 
{ 
    string str = "geeksforgeeks"; 
    str= reverseStr(str); 
    Console.WriteLine(str); 
} 
} 
  
// This code is contributed by Princi Singh 

PHP

<?php 
// A Simple Iterative PHP  
// program to reverse 
// a string 
  
// Function to reverse a string 
function reverseStr(&$str) 
{ 
    $n = strlen($str); 
  
    // Swap character starting  
    // from two corners 
    for ($i = 0; $i < $n / 2; $i++) 
        //swap the string 
        list($str[$i],  
             $str[$n - $i - 1]) = array($str[$n - $i - 1],  
                                        $str[$i]); 
} 
  
// Driver Code 
$str = "geeksforgeeks"; 
  
reverseStr($str); 
echo $str; 
  
// This code is contributed by ajit 
?> 

Output:

skeegrofskeeg

Time complexity : O(n)
Auxiliary Space : O(1)

Method 3 (Iterative using two pointers)

C++

// A Simple Iterative C++ program to reverse 
// a string 
#include <bits/stdc++.h> 
using namespace std; 
  
// Function to reverse a string 
void reverseStr(string& str) 
{ 
    int n = str.length(); 
  
    // Swap character starting from two 
    // corners 
    for (int i=0, j=n-1; i<j; i++,j--) 
        swap(str[i], str[j]);   
} 
  
// Driver program 
int main() 
{ 
    string str = "geeksforgeeks"; 
    reverseStr(str); 
    cout << str; 
    return 0; 
} 

Java

//A Simple Iterative Java program to reverse 
//a string 
class GFG { 
  
    //Function to reverse a string 
    static void reverseStr(String str) 
    { 
     int n = str.length(); 
     char []ch = str.toCharArray(); 
     char temp; 
  
     // Swap character starting from two 
     // corners 
     for (int i=0, j=n-1; i<j; i++,j--) 
     { 
         temp = ch[i]; 
         ch[i] = ch[j]; 
         ch[j] = temp; 
     } 
          
       
     System.out.println(ch); 
    } 
  
    //Driver program 
    public static void main(String[] args) { 
          
        String str = "geeksforgeeks"; 
         reverseStr(str); 
    } 
} 
// This code is contributed by Ita_c.  

Python3

# A Simple Iterative Python program to  
# reverse a string 
  
# Function to reverse a string 
def reverseStr(str): 
    n = len(str) 
  
    i, j = 0, n-1
  
    # Swap character starting from 
    # two corners 
    while i < j: 
        str[i], str[j] = str[j], str[i] 
  
        i += 1
        j -= 1
  
  
# Driver code 
if __name__ == "__main__": 
    str = "geeksforgeeks"
  
    # converting string to list 
    # because strings do not support 
    # item assignment 
    str = list(str) 
    reverseStr(str) 
  
    # converting list to string 
    str = ''.join(str) 
  
    print(str) 
  
# This code is contributed by 
# sanjeev2552 

C#

// A Simple Iterative C# program   
// to reverse a string  
using System; 
  
class GFG  
{  
  
    //Function to reverse a string  
    static void reverseStr(String str)  
    {  
        int n = str.Length;  
        char []ch = str.ToCharArray();  
        char temp;  
  
        // Swap character starting from two  
        // corners  
        for (int i=0, j=n-1; i<j; i++,j--)  
        {  
            temp = ch[i];  
            ch[i] = ch[j];  
            ch[j] = temp;  
        }  
        Console.WriteLine(ch);  
    }  
  
    //Driver program  
    public static void Main(String[] args) 
    {  
        String str = "geeksforgeeks";  
        reverseStr(str);  
    }  
}  
  
// This code is contributed by PrinciRaj1992 

PHP

<?php 
// A Simple Iterative PHP  
// program to reverse a string 
  
// Function to reverse a string 
function reverseStr (&$str) 
{ 
    $n = strlen($str); 
  
    // Swap character starting 
    // from two corners 
    for ($i = 0, $j = $n - 1;  
         $i < $j; $i++, $j--) 
        //swap function  
        list($str[$i],  
             $str[$j]) = array($str[$j],  
                               $str[$i]); 
} 
  
// Driver Code 
$str = "geeksforgeeks"; 
reverseStr($str); 
echo $str; 
  
// This code is contributed by ajit. 
?> 

Output:

skeegrofskeeg

Time complexity : O(n)
Auxiliary Space : O(1)

Method 4 (Recursive)

C++

// Recursive C++ program to reverse a string 
#include <bits/stdc++.h> 
using namespace std; 
  
void recursiveReverse(string &str, int i = 0) 
{ 
    int n = str.length(); 
    if (i == n / 2) 
        return; 
    swap(str[i], str[n - i - 1]); 
    recursiveReverse(str, i + 1); 
} 
  
// Driver program 
int main() 
{ 
    string str = "geeksforgeeks"; 
    recursiveReverse(str); 
    cout << str; 
    return 0; 
} 

Java

// Recursive Java program to reverse a string 
class GFG  
{ 
  
static void recursiveReverse(char[] str, int i) 
{ 
    int n = str.length; 
    if (i == n / 2) 
        return; 
    swap(str,i,n - i - 1); 
    recursiveReverse(str, i + 1); 
} 
static char[] swap(char []arr, int i, int j) 
{ 
    char temp= arr[i]; 
    arr[i]=arr[j]; 
    arr[j]=temp; 
    return arr; 
}  
  
// Driver program 
public static void main(String[] args)  
{ 
    char[] str = "geeksforgeeks".toCharArray(); 
    recursiveReverse(str,0); 
    System.out.println(String.valueOf(str)); 
} 
} 
  
// This code is contributed by 29AjayKumar 

Python3

# Recursive Python program to reverse a string 
  
def recursiveReverse(str, i = 0): 
    n = len(str) 
  
    if i == n // 2: 
        return
      
    str[i], str[n-i-1] = str[n-i-1], str[i] 
  
    recursiveReverse(str, i+1) 
  
if __name__ == "__main__": 
    str = "geeksforgeeks"
  
    # converting string to list 
    # because strings do not support 
    # item assignment 
    str = list(str) 
    recursiveReverse(str) 
  
    # converting list to string 
    str = ''.join(str) 
    print(str) 
  
# This code is contributed by  
# sanjeev2552 

C#

// Recursive C# program to reverse a string 
using System; 
  
public class GFG  
{ 
   
static void recursiveReverse(char[] str, int i) 
{ 
    int n = str.Length; 
    if (i == n / 2) 
        return; 
    swap(str,i,n - i - 1); 
    recursiveReverse(str, i + 1); 
} 
static char[] swap(char []arr, int i, int j) 
{ 
    char temp= arr[i]; 
    arr[i]=arr[j]; 
    arr[j]=temp; 
    return arr; 
}  
   
// Driver program 
public static void Main(String[] args)  
{ 
    char[] str = "geeksforgeeks".ToCharArray(); 
    recursiveReverse(str,0); 
    Console.WriteLine(String.Join("",str)); 
} 
} 
// This code is contributed by Princi Singh 

Because C# code not available

Output:

skeegrofskeeg

Time complexity : O(n)
Auxiliary Space : O(n)

Method 5 (Library function)

C++

// A quickly written program for reversing a string 
// using reverse() 
#include<bits/stdc++.h> 
using namespace std; 
int main() 
{ 
   string str = "geeksforgeeks"; 
      
   // Reverse str[beign..end] 
   reverse(str.begin(),str.end()); 
      
   cout << str; 
   return 0; 
} 

Java

// A Simple Java program  
// to reverse a string 
  
class GFG 
{ 
  
    public static void main(String[] args)  
    { 
        String str = "geeksforgeeks"; 
          
        // Reverse str[beign..end]  
        str = reverse(str); 
  
        System.out.println(str); 
    } 
  
    static String reverse(String input)  
    { 
        char[] temparray = input.toCharArray(); 
        int left, right = 0; 
        right = temparray.length - 1; 
  
        for (left = 0; left < right; left++, right--)  
        { 
            // Swap values of left and right  
            char temp = temparray[left]; 
            temparray[left] = temparray[right]; 
            temparray[right] = temp; 
        } 
        return String.valueOf(temparray); 
    } 
}  
  
// This code is contributed by 29AjayKumar 

Python

# A Simple python program  
# to reverse a string 
  
# Function to  
# reverse a string 
def reverseStr(str): 
      
    # print the string 
    # from last 
    print(str[::-1])      
  
# Driver Code  
def main(): 
    str = "geeksforgeeks"; 
    reverseStr(str); 
      
if __name__=="__main__": 
    main()      
      
# This code is contributed  
# by prabhat kumar singh  

C#

// A Simple C# program to reverse a string 
using System; 
      
class GFG 
{ 
  
    public static void Main(String[] args)  
    { 
        String str = "geeksforgeeks"; 
          
        // Reverse str[beign..end]  
        str = reverse(str); 
  
        Console.WriteLine(str); 
    } 
  
    static String reverse(String input)  
    { 
        char[] temparray = input.ToCharArray(); 
        int left, right = 0; 
        right = temparray.Length - 1; 
  
        for (left = 0; left < right; left++, right--)  
        { 
            // Swap values of left and right  
            char temp = temparray[left]; 
            temparray[left] = temparray[right]; 
            temparray[right] = temp; 
        } 
        return String.Join("",temparray); 
    } 
} 
  
/* This code is contributed by PrinciRaj1992 */

PHP

<?php 
// A Simple PHP program 
// to reverse a string 
  
// Function to reverse a string 
function reverseStr($str) 
{ 
  
    // print the string 
    // from last 
    echo strrev($str); 
} 
  
// Driver Code 
$str = "geeksforgeeks"; 
  
reverseStr($str); 
  
// This code is contributed 
// by Srathore 
?> 

Output:

skeegrofskeeg

My Personal Notes

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