Reverse a String – Complete Tutorial
Last Updated :
11 Jul, 2025
Given a string s, the task is to reverse the string. Reversing a string means rearranging the characters such that the first character becomes the last, the second character becomes second last and so on.
Examples:
Input: s = "GeeksforGeeks"
Output: "skeeGrofskeeG"
Explanation : The first character G moves to last position, the second character e moves to second-last and so on.
Input: s = "abdcfe"
Output: "efcdba"
Explanation: The first character a moves to last position, the second character b moves to second-last and so on.
Using backward traversal – O(n) Time and O(n) Space
The idea is to start at the last character of the string and move backward, appending each character to a new string res. This new string res will contain the characters of the original string in reverse order.
C++
// C++ program to reverse a string using backward traversal
#include <iostream>
#include <string>
using namespace std;
string reverseString(string& s) {
string res;
// Traverse on s in backward direction
// and add each charecter to a new string
for (int i = s.size() - 1; i >= 0; i--) {
res += s[i];
}
return res;
}
int main() {
string s = "abdcfe";
string res = reverseString(s);
cout << res;
return 0;
}
// C program to reverse a string using backward traversal
#include <stdio.h>
#include <string.h>
char *reverseString(char *s) {
int n = strlen(s);
char *res = (char *)malloc((n + 1) * sizeof(char));
int j = 0;
// Traverse on s in backward direction
// and add each character to a new string
for (int i = n - 1; i >= 0; i--) {
res[j] = s[i];
j++;
}
// Null-terminate the result string
res[n] = '\0';
return res;
}
int main() {
char s[] = "abdcfe";
char *res = reverseString(s);
printf("%s", res);
return 0;
}
// Java program to reverse a string using backward traversal
class GfG {
static String reverseString(String s) {
StringBuilder res = new StringBuilder();
// Traverse on s in backward direction
// and add each character to a new string
for (int i = s.length() - 1; i >= 0; i--) {
res.append(s.charAt(i));
}
return res.toString();
}
public static void main(String[] args) {
String s = "abdcfe";
String res = reverseString(s);
System.out.print(res);
}
}
# Python program to reverse a string using backward traversal
def reverseString(s):
res = []
# Traverse on s in backward direction
# and add each character to the list
for i in range(len(s) - 1, -1, -1):
res.append(s[i])
# Convert list back to string
return ''.join(res)
if __name__ == "__main__":
s = "abdcfe"
print(reverseString(s))
// C# program to reverse a string using backward traversal
using System;
using System.Text;
class GfG {
static string reverseString(string s) {
StringBuilder res = new StringBuilder();
// Traverse on s in backward direction
// and add each character to a new string
for (int i = s.Length - 1; i >= 0; i--) {
res.Append(s[i]);
}
// Convert StringBuilder to string
return res.ToString();
}
static void Main(string[] args) {
string s = "abdcfe";
string res = reverseString(s);
Console.WriteLine(res);
}
}
// JavaScript program to reverse a string using backward traversal
function reverseString(s) {
let res = [];
// Traverse on s in backward direction
// and add each character to the array
for (let i = s.length - 1; i >= 0; i--) {
res.push(s[i]);
}
return res.join('');
}
const s = "abdcfe";
console.log(reverseString(s));
Time Complexity: O(n) for backward traversal
Auxiliary Space: O(n) for storing the reversed string.
Using Two Pointers - O(n) Time and O(1) Space
The idea is to maintain two pointers: left and right, such that left points to the beginning of the string and right points to the end of the string.
While left pointer is less than the right pointer, swap the characters at these two positions. After each swap, increment the left pointer and decrement the right pointer to move towards the center of the string. This will swap all the characters in the first half with their corresponding character in the second half.
Illustration:
C++
// C++ program to reverse a string using two pointers
#include <bits/stdc++.h>
using namespace std;
string reverseString(string &s) {
int left = 0, right = s.length() - 1;
// Swap characters from both ends till we reach
// the middle of the string
while (left < right) {
swap(s[left], s[right]);
left++;
right--;
}
return s;
}
int main() {
string s = "abdcfe";
cout << reverseString(s);
return 0;
}
// C program to reverse a string using two pointers
#include <stdio.h>
#include <string.h>
char* reverseString(char *s) {
int left = 0, right = strlen(s) - 1;
// Swap characters from both ends till we reach
// the middle of the string
while (left < right) {
char temp = s[left];
s[left] = s[right];
s[right] = temp;
left++;
right--;
}
return s;
}
int main() {
char s[] = "abdcfe";
printf("%s", reverseString(s));
return 0;
}
// Java program to reverse a string using two pointers
class GfG {
static String reverseString(String s) {
int left = 0, right = s.length() - 1;
// Use StringBuilder for mutability
StringBuilder res = new StringBuilder(s);
// Swap characters from both ends till we reach
// the middle of the string
while (left < right) {
char temp = res.charAt(left);
res.setCharAt(left, res.charAt(right));
res.setCharAt(right, temp);
left++;
right--;
}
// Convert StringBuilder back to string
return res.toString();
}
public static void main(String[] args) {
String s = "abdcfe";
System.out.println(reverseString(s));
}
}
# Python program to reverse a string using two pointers
# Function to reverse a string using two pointers
def reverseString(s):
left = 0
right = len(s) - 1
# Convert string to a list for mutability
s = list(s)
# Swap characters from both ends till we reach
# the middle of the string
while left < right:
s[left], s[right] = s[right], s[left]
left += 1
right -= 1
# Convert list back to string
return ''.join(s)
if __name__ == "__main__":
s = "abdcfe"
print(reverseString(s))
// C# program to reverse a string using two pointers
using System;
using System.Text;
class GfG {
static string reverseString(string s) {
// Use StringBuilder for mutability
StringBuilder res = new StringBuilder(s);
int left = 0, right = res.Length - 1;
// Swap characters from both ends till we reach
// the middle of the string
while (left < right) {
char temp = res[left];
res[left] = res[right];
res[right] = temp;
left++;
right--;
}
// Convert StringBuilder back to string
return res.ToString();
}
static void Main(string[] args) {
string s = "abdcfe";
Console.WriteLine(reverseString(s));
}
}
// JavaScript program to reverse a string using two pointers
function reverseString(s) {
let left = 0, right = s.length - 1;
// Convert string to array for mutability
s = s.split('');
// Swap characters from both ends till we reach
// the middle of the string
while (left < right) {
[s[left], s[right]] = [s[right], s[left]];
left++;
right--;
}
return s.join('');
}
const s = "abdcfe";
console.log(reverseString(s));
Time Complexity: O(n)
Auxiliary Space: O(1)
Using Recursion - O(n) Time and O(n) Space
The idea is to use recursion and define a recursive function that takes a string as input and reverses it. Inside the recursive function,
- Swap the first and last element.
- Recursively call the function with the remaining substring.
C++
// C++ Program to reverse an array using Recursion
#include <iostream>
#include <vector>
using namespace std;
// recursive function to reverse a string from l to r
void reverseStringRec(string &s, int l, int r) {
// If the substring is empty, return
if(l >= r)
return;
swap(s[l], s[r]);
// Recur for the remaining string
reverseStringRec(s, l + 1, r - 1);
}
// function to reverse a string
string reverseString(string &s) {
int n = s.length();
reverseStringRec(s, 0, n - 1);
return s;
}
int main() {
string s = "abdcfe";
cout << reverseString(s) << endl;
return 0;
}
// C program to reverse a string using Recursion
#include <stdio.h>
#include <string.h>
// Recursive function to reverse a string from l to r
void reverseStringRec(char *s, int l, int r) {
if (l >= r)
return;
// Swap the characters at the ends
char temp = s[l];
s[l] = s[r];
s[r] = temp;
// Recur for the remaining string
reverseStringRec(s, l + 1, r - 1);
}
char* reverseString(char *s) {
int n = strlen(s);
reverseStringRec(s, 0, n - 1);
return s;
}
int main() {
char s[] = "abdcfe";
printf("%s\n", reverseString(s));
return 0;
}
// Java program to reverse a string using Recursion
class GfG {
// Recursive function to reverse a string from l to r
static void reverseStringRec(char[] s, int l, int r) {
if (l >= r)
return;
// Swap the characters at the ends
char temp = s[l];
s[l] = s[r];
s[r] = temp;
// Recur for the remaining string
reverseStringRec(s, l + 1, r - 1);
}
// Function to reverse a string
static String reverseString(String s) {
char[] arr = s.toCharArray();
reverseStringRec(arr, 0, arr.length - 1);
return new String(arr);
}
public static void main(String[] args) {
String s = "abdcfe";
System.out.println(reverseString(s));
}
}
# Python program to reverse a string using Recursion
# Recursive Function to reverse a string
def reverseStringRec(arr, l, r):
if l >= r:
return
# Swap the characters at the ends
arr[l], arr[r] = arr[r], arr[l]
# Recur for the remaining string
reverseStringRec(arr, l + 1, r - 1)
def reverseString(s):
# Convert string to list of characters
arr = list(s)
reverseStringRec(arr, 0, len(arr) - 1)
# Convert list back to string
return ''.join(arr)
if __name__ == "__main__":
s = "abdcfe"
print(reverseString(s))
// C# program to reverse a string using Recursion
using System;
using System.Text;
class GfG {
// recursive function to reverse a string from l to r
static void reverseStringRec(StringBuilder s, int l, int r) {
if (l >= r)
return;
char temp = s[l];
s[l] = s[r];
s[r] = temp;
// Recur for the remaining string
reverseStringRec(s, l + 1, r - 1);
}
// function to reverse a string
static string reverseString(string input) {
StringBuilder s = new StringBuilder(input);
int n = s.Length;
reverseStringRec(s, 0, n - 1);
return s.ToString();
}
static void Main() {
string s = "abdcfe";
Console.WriteLine(reverseString(s));
}
}
// JavaScript program to reverse a string using Recursion
// Recursive Function to reverse a string
function reverseStringRec(res, l, r) {
if (l >= r) return;
// Swap the characters at the ends
[res[l], res[r]] = [res[r], res[l]];
// Recur for the remaining string
reverseStringRec(res, l + 1, r - 1);
}
function reverseString(s) {
// Convert string to array of characters
let res = s.split('');
reverseStringRec(res, 0, res.length - 1);
// Convert array back to string
return res.join('');
}
let s = "abdcfe";
console.log(reverseString(s));
Time Complexity: O(n) where n is length of string
Auxiliary Space: O(n)
Using Stack - O(n) Time and O(n) Space
The idea is to use stack for reversing a string because Stack follows Last In First Out (LIFO) principle. This means the last character you add is the first one you'll take out. So, when we push all the characters of a string into the stack, the last character becomes the first one to pop.
Illustration:
C++
// C++ program to reverse a string using stack
#include <bits/stdc++.h>
using namespace std;
string reverseString(string &s) {
stack<char> st;
// Push the charcters into stack
for (int i = 0; i < s.size(); i++) {
st.push(s[i]);
}
// Pop the characters of stack into the original string
for (int i = 0; i < s.size(); i++) {
s[i] = st.top();
st.pop();
}
return s;
}
int main() {
string s = "abdcfe";
cout << reverseString(s);
return 0;
}
// Java program to reverse a string using stack
import java.util.*;
class GfG {
static String reverseString(String s) {
Stack<Character> st = new Stack<>();
// Push the characters into stack
for (int i = 0; i < s.length(); i++)
st.push(s.charAt(i));
StringBuilder res = new StringBuilder();
// Pop the characters of stack into the original string
for (int i = 0; i < s.length(); i++)
res.append(st.pop());
return res.toString();
}
public static void main(String[] args) {
String s = "abdcfe";
System.out.println(reverseString(s));
}
}
# Python program to reverse a string using stack
def reverseString(s):
stack = []
# Push the characters into stack
for char in s:
stack.append(char)
# Prepare a list to hold the reversed characters
rev = [''] * len(s)
# Pop the characters from stack into the reversed list
for i in range(len(s)):
rev[i] = stack.pop()
# Join the list to form the reversed string
return ''.join(rev)
if __name__ == "__main__":
s = "abdcfe"
print(reverseString(s))
// C# program to reverse a string using stack
using System;
using System.Collections.Generic;
using System.Text;
class GfG {
static string reverseString(string s) {
Stack<char> st = new Stack<char>();
// Push the characters into stack
for (int i = 0; i < s.Length; i++)
st.Push(s[i]);
// Create a StringBuilder to hold the reversed string
StringBuilder res = new StringBuilder();
// Pop the characters from stack into the StringBuilder
while (st.Count > 0)
res.Append(st.Pop());
// Convert the StringBuilder back to a string
return res.ToString();
}
static void Main() {
string s = "abdcfe";
Console.WriteLine(reverseString(s));
}
}
// JavaScript program to reverse a string using stack
function reverseString(s) {
// To store the characters of the original string.
const stack = [];
// Push the characters into the stack.
for (let i = 0; i < s.length; i++) {
stack.push(s[i]);
}
// Create an array to hold the reversed characters
const res = new Array(s.length);
// Pop the characters of the stack and store in the array
for (let i = 0; i < s.length; i++) {
res[i] = stack.pop();
}
// Join the array to form the reversed string
return res.join('');
}
let str = "abdcfe";
console.log(reverseString(str));
Time Complexity: O(n)
Auxiliary Space: O(n)
Using Inbuilt methods - O(n) Time and O(1) Space
The idea is to use built-in reverse method to reverse the string. If built-in method for string reversal does not exist, then convert string to array or list and use their built-in method for reverse. Then convert it back to string.
C++
#include <bits/stdc++.h>
using namespace std;
string reverseString(string &s) {
reverse(s.begin(), s.end());
return s;
}
int main() {
string s = "abdcfe";
cout << reverseString(s) ;
return 0;
}
// Java program to reverse a string using StringBuffer class
import java.io.*;
import java.util.*;
class GFG {
static String stringReverse(String s) {
StringBuilder res = new StringBuilder(s);
res.reverse();
return res.toString();
}
public static void main(String[] args) {
String s = "abdcfe";
System.out.println(stringReverse(s));
}
}
# Function to reverse a string
def reverseString(s):
# Reverse the string using slicing
return s[::-1]
if __name__ == "__main__":
str = "abdcfe"
print(reverseString(str))
// C# program to reverse a string
using System;
class GfG {
static string reverseString(string s) {
// Reverse the string using the built-in method
char[] arr = s.ToCharArray();
Array.Reverse(arr);
return new string(arr);
}
static void Main() {
string s = "abdcfe";
Console.WriteLine(reverseString(s));
}
}
// Function to reverse a string
function reverseString(s) {
// convert to array to make it mutable
s = s.split('');
// Reverse the string using the built-in method
s = s.reverse();
return s.join('');
}
let str = "abdcfe";
console.log(reverseString(str));
Time Complexity: O(n)
Auxiliary Space: O(1) in C++ and python and O(n) in Java, C# and JavaScript (extra space is used to store in array or list or StringBuilder for reversal).
Reverse A String in Python
C++ Program to Reverse a String
Similar Reads
Basics & Prerequisites
Data Structures
Array Data StructureIn this article, we introduce array, implementation in different popular languages, its basic operations and commonly seen problems / interview questions. An array stores items (in case of C/C++ and Java Primitive Arrays) or their references (in case of Python, JS, Java Non-Primitive) at contiguous
3 min read
String in Data StructureA string is a sequence of characters. The following facts make string an interesting data structure.Small set of elements. Unlike normal array, strings typically have smaller set of items. For example, lowercase English alphabet has only 26 characters. ASCII has only 256 characters.Strings are immut
2 min read
Hashing in Data StructureHashing is a technique used in data structures that efficiently stores and retrieves data in a way that allows for quick access. Hashing involves mapping data to a specific index in a hash table (an array of items) using a hash function. It enables fast retrieval of information based on its key. The
2 min read
Linked List Data StructureA linked list is a fundamental data structure in computer science. It mainly allows efficient insertion and deletion operations compared to arrays. Like arrays, it is also used to implement other data structures like stack, queue and deque. Here’s the comparison of Linked List vs Arrays Linked List:
2 min read
Stack Data StructureA Stack is a linear data structure that follows a particular order in which the operations are performed. The order may be LIFO(Last In First Out) or FILO(First In Last Out). LIFO implies that the element that is inserted last, comes out first and FILO implies that the element that is inserted first
2 min read
Queue Data StructureA Queue Data Structure is a fundamental concept in computer science used for storing and managing data in a specific order. It follows the principle of "First in, First out" (FIFO), where the first element added to the queue is the first one to be removed. It is used as a buffer in computer systems
2 min read
Tree Data StructureTree Data Structure is a non-linear data structure in which a collection of elements known as nodes are connected to each other via edges such that there exists exactly one path between any two nodes. Types of TreeBinary Tree : Every node has at most two childrenTernary Tree : Every node has at most
4 min read
Graph Data StructureGraph Data Structure is a collection of nodes connected by edges. It's used to represent relationships between different entities. If you are looking for topic-wise list of problems on different topics like DFS, BFS, Topological Sort, Shortest Path, etc., please refer to Graph Algorithms. Basics of
3 min read
Trie Data StructureThe Trie data structure is a tree-like structure used for storing a dynamic set of strings. It allows for efficient retrieval and storage of keys, making it highly effective in handling large datasets. Trie supports operations such as insertion, search, deletion of keys, and prefix searches. In this
15+ min read
Algorithms
Searching AlgorithmsSearching algorithms are essential tools in computer science used to locate specific items within a collection of data. In this tutorial, we are mainly going to focus upon searching in an array. When we search an item in an array, there are two most common algorithms used based on the type of input
2 min read
Sorting AlgorithmsA Sorting Algorithm is used to rearrange a given array or list of elements in an order. For example, a given array [10, 20, 5, 2] becomes [2, 5, 10, 20] after sorting in increasing order and becomes [20, 10, 5, 2] after sorting in decreasing order. There exist different sorting algorithms for differ
3 min read
Introduction to RecursionThe process in which a function calls itself directly or indirectly is called recursion and the corresponding function is called a recursive function. A recursive algorithm takes one step toward solution and then recursively call itself to further move. The algorithm stops once we reach the solution
14 min read
Greedy AlgorithmsGreedy algorithms are a class of algorithms that make locally optimal choices at each step with the hope of finding a global optimum solution. At every step of the algorithm, we make a choice that looks the best at the moment. To make the choice, we sometimes sort the array so that we can always get
3 min read
Graph AlgorithmsGraph is a non-linear data structure like tree data structure. The limitation of tree is, it can only represent hierarchical data. For situations where nodes or vertices are randomly connected with each other other, we use Graph. Example situations where we use graph data structure are, a social net
3 min read
Dynamic Programming or DPDynamic Programming is an algorithmic technique with the following properties.It is mainly an optimization over plain recursion. Wherever we see a recursive solution that has repeated calls for the same inputs, we can optimize it using Dynamic Programming. The idea is to simply store the results of
3 min read
Bitwise AlgorithmsBitwise algorithms in Data Structures and Algorithms (DSA) involve manipulating individual bits of binary representations of numbers to perform operations efficiently. These algorithms utilize bitwise operators like AND, OR, XOR, NOT, Left Shift, and Right Shift.BasicsIntroduction to Bitwise Algorit
4 min read
Advanced
Segment TreeSegment Tree is a data structure that allows efficient querying and updating of intervals or segments of an array. It is particularly useful for problems involving range queries, such as finding the sum, minimum, maximum, or any other operation over a specific range of elements in an array. The tree
3 min read
Pattern SearchingPattern searching algorithms are essential tools in computer science and data processing. These algorithms are designed to efficiently find a particular pattern within a larger set of data. Patten SearchingImportant Pattern Searching Algorithms:Naive String Matching : A Simple Algorithm that works i
2 min read
GeometryGeometry is a branch of mathematics that studies the properties, measurements, and relationships of points, lines, angles, surfaces, and solids. From basic lines and angles to complex structures, it helps us understand the world around us.Geometry for Students and BeginnersThis section covers key br
2 min read
Interview Preparation
Practice Problem