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++ 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 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 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# 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 |
<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.
// 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;
} |
// 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 |
# Reversing a string using reverse() str = "geeksforgeeks" ;
# Reverse str[begin..end] str = "".join( reversed ( str ))
print ( str );
# This code is contributed by 29AjayKumar |
// 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 |
<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.