Given an array (or string), the task is to reverse the array/string.
Examples :
Input : arr[] = {1, 2, 3}
Output : arr[] = {3, 2, 1}
Input : arr[] = {4, 5, 1, 2}
Output : arr[] = {2, 1, 5, 4}
Iterative way :
1) Initialize start and end indexes as start = 0, end = n-1
2) In a loop, swap arr[start] with arr[end] and change start and end as follows :
start = start +1, end = end – 1
Another example to reverse a string:
Below is the implementation of the above approach :
C++
// Iterative C++ program to reverse an array #include <bits/stdc++.h> using namespace std; /* Function to reverse arr[] from start to end*/void rvereseArray(int arr[], int start, int end) { while (start < end) { int temp = arr[start]; arr[start] = arr[end]; arr[end] = temp; start++; end--; } } /* Utility function to print an array */void printArray(int arr[], int size) { for (int i = 0; i < size; i++) cout << arr[i] << " "; cout << endl; } /* Driver function to test above functions */int main() { int arr[] = {1, 2, 3, 4, 5, 6}; int n = sizeof(arr) / sizeof(arr[0]); // To print original array printArray(arr, n); // Function calling rvereseArray(arr, 0, n-1); cout << "Reversed array is" << endl; // To print the Reversed array printArray(arr, n); return 0; } |
C
// Iterative C program to reverse an array #include<stdio.h> /* Function to reverse arr[] from start to end*/void rvereseArray(int arr[], int start, int end) { int temp; while (start < end) { temp = arr[start]; arr[start] = arr[end]; arr[end] = temp; start++; end--; } } /* Utility that prints out an array on a line */void printArray(int arr[], int size) { int i; for (i=0; i < size; i++) printf("%d ", arr[i]); printf("\n"); } /* Driver function to test above functions */int main() { int arr[] = {1, 2, 3, 4, 5, 6}; int n = sizeof(arr) / sizeof(arr[0]); printArray(arr, n); rvereseArray(arr, 0, n-1); printf("Reversed array is \n"); printArray(arr, n); return 0; } |
Java
// Iterative java program to reverse an // array public class GFG { /* Function to reverse arr[] from start to end*/ static void rvereseArray(int arr[], int start, int end) { int temp; while (start < end) { temp = arr[start]; arr[start] = arr[end]; arr[end] = temp; start++; end--; } } /* Utility that prints out an array on a line */ static void printArray(int arr[], int size) { for (int i = 0; i < size; i++) System.out.print(arr[i] + " "); System.out.println(); } // Driver code public static void main(String args[]) { int arr[] = {1, 2, 3, 4, 5, 6}; printArray(arr, 6); rvereseArray(arr, 0, 5); System.out.print("Reversed array is \n"); printArray(arr, 6); } } // This code is contributed by Sam007 |
Python
# Iterative python program to reverse an array # Function to reverse A[] from start to end def reverseList(A, start, end): while start < end: A[start], A[end] = A[end], A[start] start += 1 end -= 1 # Driver function to test above function A = [1, 2, 3, 4, 5, 6] print(A) reverseList(A, 0, 5) print("Reversed list is") print(A) # This program is contributed by Pratik Chhajer |
C#
// Iterative C# program to reverse an // array using System; class GFG { /* Function to reverse arr[] from start to end*/ static void rvereseArray(int []arr, int start, int end) { int temp; while (start < end) { temp = arr[start]; arr[start] = arr[end]; arr[end] = temp; start++; end--; } } /* Utility that prints out an array on a line */ static void printArray(int []arr, int size) { for (int i = 0; i < size; i++) Console.Write(arr[i] + " "); Console.WriteLine(); } // Driver function public static void Main() { int []arr = {1, 2, 3, 4, 5, 6}; printArray(arr, 6); rvereseArray(arr, 0, 5); Console.Write("Reversed array is \n"); printArray(arr, 6); } } // This code is contributed by Sam007 |
PHP
<?php // Iterative PHP program // to reverse an array /* Function to reverse $arr from start to end*/function rvereseArray(&$arr, $start, $end) { while ($start < $end) { $temp = $arr[$start]; $arr[$start] = $arr[$end]; $arr[$end] = $temp; $start++; $end--; } } /* Utility function to print an array */function printArray(&$arr, $size) { for ($i = 0; $i < $size; $i++) echo $arr[$i] . " "; echo "\n"; } // Driver code $arr = array(1, 2, 3, 4, 5, 6); // To print original array printArray($arr, 6); // Function calling rvereseArray($arr, 0, 5); echo "Reversed array is" ."\n"; // To print the Reversed array printArray($arr, 6); // This code is contributed // by ChitraNayal ?> |
javascript
// Iterative Javascript program to reverse an array /* Function to reverse arr[] from start to end*/function rvereseArray(arr,start,end) { while (start < end) { var temp = arr[start]; arr[start] = arr[end]; arr[end] = temp; start++; end--; } } /* Utility function to print an array */function printArray(arr,size) { for (var i = 0; i < size; i++){ console.log(arr[i]); } } /* Driver function to test above functions */ var arr= [1, 2, 3, 4, 5, 6]; var n = 6; // To print original array printArray(arr, n); // Function calling rvereseArray(arr, 0, n-1); console.log("Reversed array is"); // To print the Reversed array printArray(arr, n); |
Output :
1 2 3 4 5 6 Reversed array is 6 5 4 3 2 1
Time Complexity: O(n)
Auxiliary Space: O(1)
Recursive Way :
1) Initialize start and end indexes as start = 0, end = n-1
2) Swap arr[start] with arr[end]
3) Recursively call reverse for rest of the array.
Below is the implementation of the above approach :
C++
// Recursive C++ program to reverse an array #include <bits/stdc++.h> using namespace std; /* Function to reverse arr[] from start to end*/void rvereseArray(int arr[], int start, int end) { if (start >= end) return; int temp = arr[start]; arr[start] = arr[end]; arr[end] = temp; // Recursive Function calling rvereseArray(arr, start + 1, end - 1); } /* Utility function to print an array */void printArray(int arr[], int size) { for (int i = 0; i < size; i++) cout << arr[i] << " "; cout << endl; } /* Driver function to test above functions */int main() { int arr[] = {1, 2, 3, 4, 5, 6}; // To print original array printArray(arr, 6); // Function calling rvereseArray(arr, 0, 5); cout << "Reversed array is" << endl; // To print the Reversed array printArray(arr, 6); return 0; } |
C
// Recursive C program to reverse an array #include <stdio.h> /* Function to reverse arr[] from start to end*/void rvereseArray(int arr[], int start, int end) { int temp; if (start >= end) return; temp = arr[start]; arr[start] = arr[end]; arr[end] = temp; rvereseArray(arr, start+1, end-1); } /* Utility that prints out an array on a line */void printArray(int arr[], int size) { int i; for (i=0; i < size; i++) printf("%d ", arr[i]); printf("\n"); } /* Driver function to test above functions */int main() { int arr[] = {1, 2, 3, 4, 5, 6}; printArray(arr, 6); rvereseArray(arr, 0, 5); printf("Reversed array is \n"); printArray(arr, 6); return 0; } |
Java
// Recursive Java Program to reverse an array import java.io.*; class ReverseArray { /* Function to reverse arr[] from start to end*/ static void rvereseArray(int arr[], int start, int end) { int temp; if (start >= end) return; temp = arr[start]; arr[start] = arr[end]; arr[end] = temp; rvereseArray(arr, start+1, end-1); } /* Utility that prints out an array on a line */ static void printArray(int arr[], int size) { for (int i=0; i < size; i++) System.out.print(arr[i] + " "); System.out.println(""); } /*Driver function to check for above functions*/ public static void main (String[] args) { int arr[] = {1, 2, 3, 4, 5, 6}; printArray(arr, 6); rvereseArray(arr, 0, 5); System.out.println("Reversed array is "); printArray(arr, 6); } } /*This article is contributed by Devesh Agrawal*/ |
Python
# Recursive python program to reverse an array # Function to reverse A[] from start to end def reverseList(A, start, end): if start >= end: return A[start], A[end] = A[end], A[start] reverseList(A, start+1, end-1) # Driver function to test above function A = [1, 2, 3, 4, 5, 6] print(A) reverseList(A, 0, 5) print("Reversed list is") print(A) # This program is contributed by Pratik Chhajer |
C#
// C# program to reverse an array using System; class GFG { /* Function to reverse arr[] from start to end*/ static void rvereseArray(int []arr, int start, int end) { int temp; if (start >= end) return; temp = arr[start]; arr[start] = arr[end]; arr[end] = temp; rvereseArray(arr, start+1, end-1); } /* Utility that prints out an array on a line */ static void printArray(int []arr, int size) { for (int i = 0; i < size; i++) Console.Write(arr[i] + " "); Console.WriteLine(""); } // Driver Code public static void Main () { int []arr = {1, 2, 3, 4, 5, 6}; printArray(arr, 6); rvereseArray(arr, 0, 5); Console.WriteLine("Reversed array is "); printArray(arr, 6); } } // This code is contributed by Sam007 |
PHP
<?php // Iterative PHP program // to reverse an array /* Function to reverse $arr from start to end*/function rvereseArray(&$arr, $start, $end) { if ($start >= $end) return; $temp = $arr[$start]; $arr[$start] = $arr[$end]; $arr[$end] = $temp; //Recursive Function calling rvereseArray($arr, $start + 1, $end - 1); } /* Utility function to print an array */function printArray(&$arr, $size) { for ($i = 0; $i < $size; $i++) echo $arr[$i] . " "; echo "\n"; } // Driver code $arr = array(1, 2, 3, 4, 5, 6); // To print original array printArray($arr, 6); // Function calling rvereseArray($arr, 0, 5); echo "Reversed array is" ."\n"; // To print the Reversed array printArray($arr, 6); // This code is contributed // by ChitraNayal ?> |
javascript
// Recursive Javascript program to reverse an array /* Function to reverse arr[] from start to end*/function rvereseArray(arr,start,end) { var temp = arr[start]; arr[start] = arr[end]; arr[end] = temp; // Recursive Function calling if (start+1<end-1){ rvereseArray(arr, start + 1, end - 1); } } /* Utility function to print an array */function printArray(arr,size) { for (var i = 0; i < size; i++){ console.log(arr[i]); } } /* Driver function to test above functions */ var arr= [1, 2, 3, 4, 5, 6]; // To print original array printArray(arr, 6); // Function calling rvereseArray(arr, 0, 5); console.log("Reversed array is"); // To print the Reversed array printArray(arr, 6); |
Output :
1 2 3 4 5 6 Reversed array is 6 5 4 3 2 1
Time Complexity: O(n)
Auxiliary Space: O(n)
Please write comments if you find any bug in the above programs or other ways to solve the same problem.
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