Reverse string without using any temporary variable

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 C++ implementation of the idea.

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// C++ Program to reverse a string without
// using temp variable
#include <bits/stdc++.h>
using namespace std;
  
// Function to reverse string and return revesed 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;
}

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Output:

 skeeGrofskeeG

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.

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// 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;
}

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Output:

 skeeGrofskeeG

This article is contributed by Mr. Somesh Awasthi. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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