Program to reverse a string (Iterative and Recursive)
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; } |
Java
// Java program to reverse a string using stack import java.util.*; class GFG { public static String recursiveReverse(char []str) { Stack<Character> st = new Stack<>(); for(int i=0; i<str.length; i++) st.push(str[i]); for (int i=0; i<str.length; i++) { str[i] = st.peek(); st.pop(); } return String.valueOf(str);// converting character array to string } // Driver program public static void main(String []args) { String str = "geeksforgeeks"; str = recursiveReverse(str.toCharArray());// passing character array as parameter System.out.println(str); } } // This code is contributed by Adarsh_Verma |
Python3
# Python program to reverse a string using stack def recursiveReverse(str): # using as stack stack = [] for i in range(len(str)): stack.append(str[i]) for i in range(len(str)): str[i] = stack.pop() if __name__ == "__main__": str = "geeksforgeeks" # converting string to list # because strings do not support # item assignment str = list(str) recursiveReverse(str) # converting list to string str = ''.join(str) print(str) # This code is contributed by # sanjeev2552 |
C#
// C# program to reverse a string using stack using System; using System.Collections.Generic; class GFG { public static String recursiveReverse(char []str) { Stack<char> st = new Stack<char>(); for(int i = 0; i < str.Length; i++) st.Push(str[i]); for (int i = 0; i < str.Length; i++) { str[i] = st.Peek(); st.Pop(); } // converting character array to string return String.Join("",str); } // Driver program public static void Main() { String str = "geeksforgeeks"; // passing character array as parameter str = recursiveReverse(str.ToCharArray()); Console.WriteLine(str); } } // This code is contributed by Rajput-Ji |
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; } |
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 |
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 |
C#
// A Simple Iterative C# program to reverse // a string using System; class GFG { // Function to reverse a string static String reverseStr(String str) { int n = str.Length; // Swap character starting from two // corners for (int i = 0; i < n / 2; i++) str = swap(str,i,n - i - 1); return str; } static String swap(String str, int i, int j) { char []ch = str.ToCharArray(); char temp = ch[i]; ch[i] = ch[j]; ch[j] = temp; return String.Join("",ch); } // Driver code public static void Main(String[] args) { string str = "geeksforgeeks"; str= reverseStr(str); Console.WriteLine(str); } } // This code is contributed by Princi Singh |
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 ?> |
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; } |
Java
//A Simple Iterative Java program to reverse //a string class GFG { //Function to reverse a string static void reverseStr(String str) { int n = str.length(); char []ch = str.toCharArray(); char temp; // Swap character starting from two // corners for (int i=0, j=n-1; i<j; i++,j--) { temp = ch[i]; ch[i] = ch[j]; ch[j] = temp; } System.out.println(ch); } //Driver program public static void main(String[] args) { String str = "geeksforgeeks"; reverseStr(str); } } // This code is contributed by Ita_c. |
Python3
# A Simple Iterative Python program to # reverse a string # Function to reverse a string def reverseStr(str): n = len(str) i, j = 0, n-1 # Swap character starting from # two corners while i < j: str[i], str[j] = str[j], str[i] i += 1 j -= 1 # Driver code if __name__ == "__main__": str = "geeksforgeeks" # converting string to list # because strings do not support # item assignment str = list(str) reverseStr(str) # converting list to string str = ''.join(str) print(str) # This code is contributed by # sanjeev2552 |
C#
// A Simple Iterative C# program // to reverse a string using System; class GFG { //Function to reverse a string static void reverseStr(String str) { int n = str.Length; char []ch = str.ToCharArray(); char temp; // Swap character starting from two // corners for (int i=0, j=n-1; i<j; i++,j--) { temp = ch[i]; ch[i] = ch[j]; ch[j] = temp; } Console.WriteLine(ch); } //Driver program public static void Main(String[] args) { String str = "geeksforgeeks"; reverseStr(str); } } // This code is contributed by PrinciRaj1992 |
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. ?> |
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; } |
Java
// Recursive Java program to reverse a string class GFG { static void recursiveReverse(char[] str, int i) { int n = str.length; if (i == n / 2) return; swap(str,i,n - i - 1); recursiveReverse(str, i + 1); } static char[] swap(char []arr, int i, int j) { char temp= arr[i]; arr[i]=arr[j]; arr[j]=temp; return arr; } // Driver program public static void main(String[] args) { char[] str = "geeksforgeeks".toCharArray(); recursiveReverse(str,0); System.out.println(String.valueOf(str)); } } // This code is contributed by 29AjayKumar |
Python3
# Recursive Python program to reverse a string def recursiveReverse(str, i = 0): n = len(str) if i == n // 2: return str[i], str[n-i-1] = str[n-i-1], str[i] recursiveReverse(str, i+1) if __name__ == "__main__": str = "geeksforgeeks" # converting string to list # because strings do not support # item assignment str = list(str) recursiveReverse(str) # converting list to string str = ''.join(str) print(str) # This code is contributed by # sanjeev2552 |
C#
// Recursive C# program to reverse a string using System; public class GFG { static void recursiveReverse(char[] str, int i) { int n = str.Length; if (i == n / 2) return; swap(str,i,n - i - 1); recursiveReverse(str, i + 1); } static char[] swap(char []arr, int i, int j) { char temp= arr[i]; arr[i]=arr[j]; arr[j]=temp; return arr; } // Driver program public static void Main(String[] args) { char[] str = "geeksforgeeks".ToCharArray(); recursiveReverse(str,0); Console.WriteLine(String.Join("",str)); } } // This code is contributed by Princi Singh |
Because C# code not available
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; } |
Java
// A Simple Java program // to reverse a string class GFG { public static void main(String[] args) { String str = "geeksforgeeks"; // Reverse str[beign..end] str = reverse(str); System.out.println(str); } static String reverse(String input) { char[] temparray = input.toCharArray(); int left, right = 0; right = temparray.length - 1; for (left = 0; left < right; left++, right--) { // Swap values of left and right char temp = temparray[left]; temparray[left] = temparray[right]; temparray[right] = temp; } return String.valueOf(temparray); } } // This code is contributed by 29AjayKumar |
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 |
C#
// A Simple C# program to reverse a string using System; class GFG { public static void Main(String[] args) { String str = "geeksforgeeks"; // Reverse str[beign..end] str = reverse(str); Console.WriteLine(str); } static String reverse(String input) { char[] temparray = input.ToCharArray(); int left, right = 0; right = temparray.Length - 1; for (left = 0; left < right; left++, right--) { // Swap values of left and right char temp = temparray[left]; temparray[left] = temparray[right]; temparray[right] = temp; } return String.Join("",temparray); } } /* This code is contributed by PrinciRaj1992 */ |
PHP
<?php // A Simple PHP program // to reverse a string // Function to reverse a string function reverseStr($str) { // print the string // from last echo strrev($str); } // Driver Code $str = "geeksforgeeks"; reverseStr($str); // This code is contributed // by Srathore ?> |
Output:
skeegrofskeeg
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