Reverse string without using any temporary variable Last Updated : 07 Jul, 2022 Comments Improve Suggest changes Like Article Like Report We are given a string. We are also given indexes of first and last characters in string. The task is to reverse the string without using any extra variable. Examples: Input : str = "abc" Output : str = "cba" Input : str = "GeeksforGeeks" Output : str = "skeeGrofskeeG" If we take a look at program to reverse a string or array, all we need to do is swap two characters. The idea is to use XOR for swapping the variable. Below is the implementation of the idea. C++ // C++ Program to reverse a string without // using temp variable #include <bits/stdc++.h> using namespace std; // Function to reverse string and return reversed string string reversingString(string str, int start, int end) { // Iterate loop upto start not equal to end while (start < end) { // XOR for swapping the variable str[start] ^= str[end]; str[end] ^= str[start]; str[start] ^= str[end]; ++start; --end; } return str; } // Driver Code int main() { string s = "GeeksforGeeks"; cout << reversingString(s, 0, 12); return 0; } Java // Java Program to reverse a string without // using temp variable import java.util.*; class GFG { // Function to reverse string and // return reversed string static String reversingString(char []str, int start, int end) { // Iterate loop upto start not equal to end while (start < end) { // XOR for swapping the variable str[start] ^= str[end]; str[end] ^= str[start]; str[start] ^= str[end]; ++start; --end; } return String.valueOf(str); } // Driver Code public static void main(String[] args) { String s = "GeeksforGeeks"; System.out.println(reversingString (s.toCharArray(), 0, 12)); } } // This code is contributed by 29AjayKumar Python3 # Python3 Program to reverse a string # without using temp variable # Function to reverse string and # return reversed string def reversingString(str, start, end): # Iterate loop upto start not equal to end while (start < end): # XOR for swapping the variable str = (str[:start] + chr(ord(str[start]) ^ ord(str[end])) + str[start + 1:]); str = (str[:end] + chr(ord(str[start]) ^ ord(str[end])) + str[end + 1:]); str = (str[:start] + chr(ord(str[start]) ^ ord(str[end])) + str[start + 1:]); start += 1; end -= 1; return str; # Driver Code s = "GeeksforGeeks"; print(reversingString(s, 0, 12)); # This code is contributed by 29AjayKumar C# // C# Program to reverse a string without // using temp variable using System; class GFG { // Function to reverse string and // return reversed string static String reversingString(char []str, int start, int end) { // Iterate loop upto start // not equal to end while (start < end) { // XOR for swapping the variable str[start] ^= str[end]; str[end] ^= str[start]; str[start] ^= str[end]; ++start; --end; } return String.Join("", str); } // Driver Code public static void Main(String[] args) { String s = "GeeksforGeeks"; Console.WriteLine(reversingString (s.ToCharArray(), 0, 12)); } } // This code is contributed by 29AjayKumar JavaScript <script> // Javascript program to reverse a string // without using temp variable // Function to reverse string and // return reversed string function reversingString(str, start, end) { // Iterate loop upto start not // equal to end while (start < end) { // XOR for swapping the variable str[start] = String.fromCharCode( str[start].charCodeAt(0) ^ str[end].charCodeAt(0)); str[end] = String.fromCharCode( str[end].charCodeAt(0) ^ str[start].charCodeAt(0)); str[start] = String.fromCharCode( str[start].charCodeAt(0) ^ str[end].charCodeAt(0)); ++start; --end; } return(str).join(""); } // Driver Code let s = "GeeksforGeeks"; document.write(reversingString( s.split(""), 0, 12)); // This code is contributed by rag2127 </script> Output: skeeGrofskeeG Time Complexity: O(n) Auxiliary Space: O(1) If we are allowed to library function, we can also use the idea discussed in quickly reverse a string in C++. We don't even need indexes of first and last characters. C++ // Reversing a string using reverse() #include<bits/stdc++.h> using namespace std; int main() { string str = "geeksforgeeks"; // Reverse str[begin..end] reverse(str.begin(), str.end()); cout << str; return 0; } Java // Reversing a string using reverse() class GFG { public static void main(String[] args) { StringBuilder str = new StringBuilder("geeksforgeeks"); // Reverse str[begin..end] str.reverse(); System.out.println(str); } } // This code is contributed // by PrinciRaj1992 Python3 # Reversing a string using reverse() str = "geeksforgeeks"; # Reverse str[begin..end] str = "".join(reversed(str)) print(str); # This code is contributed by 29AjayKumar C# // Reversing a string using reverse() using System; using System.Linq; class GFG { public static void Main(String[] args) { String str = "geeksforgeeks"; // Reverse str[begin..end] str = new string(str.Reverse().ToArray()); Console.WriteLine(str); } } // This code is contributed by 29AjayKumar JavaScript <script> // Reversing a string using reverse() function reverseString(str) { return str.split("").reverse().join(""); } var str = ("geeksforgeeks"); document.write(reverseString(str)); // This code is contributed by todaysgaurav </script> Output: skeegrofskeeg Time complexity : O(n) Auxiliary Space : O(1) This article is contributed by Aarti_Rathi and Mr. Somesh Awasthi. 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