Given a string, write a recursive program to reverse it.
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; } |
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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; } |
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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 |
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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 |
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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 $str; // This code is contributed by ajit ?> |
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Output:
skeegrofskeeg
Time complexity : O(n)
Auxiliary Space : O(1)
Method 3 (Iterative using two pointers)
C++
// A Simple Iterative C++ program to reverse // a string #include <bits/stdc++.h> using namespace std; // Function to reverse a string void reverseStr(string& str) { int n = str.length(); // Swap character starting from two // corners for (int i=0, j=n-1; i<j; i++,j--) swap(str[i], str[j]); } // Driver program int main() { string str = "geeksforgeeks"; reverseStr(str); cout << str; return 0; } |
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PHP
<?php // A Simple Iterative PHP // program to reverse a string // Function to reverse a string function reverseStr (&$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. ?> |
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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; } |
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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; } |
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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 |
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Output:
skeegrofskeeg
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