C++ Program to Reverse elements of an array
Reverse elements of an Array in C++
Here, in this page we will discuss the program to reverse elements of an Array in C++ Programming language. We are given with an array and need to reverse that array. WE will discuss various approaches to reverse the array.
Method Discussed :
- Method 1: Printing array in reverse order.
- Method 2: In-place reversing of the original array
- Method 3: Recursive in-place reversing of the original array
- Method 4 : Using inbuilt function
Method 1 (Simple Printing Array in Reverse):
Objective: Reverse array in C++
- Run a loop in reverse order i.e, from index n-1 to index 0.
- Print i-th element
Time and Space Complexity :
- Time Complexity : O(n)
- Space Complexity : O(1)
Method 1 : Code in C++
Run
#include<bits/stdc++.h>
using namespace std;
int main(){
int arr[] = {10, 20, 30, 40, 50};
int n = sizeof(arr)/sizeof(arr[0]);
for(int i=n-1; i>=0; i--)
cout<<arr[i]<<" ";
}Output
50 40 30 20 10
Method 2 (In-Place Reversal):
- Take two variables say i = 0 and j = n – 1.
- Run a loop till i < j
- swap(arr[i], arr[j])
- Increment i and decrement the j
- Now, Print the array
Time and Space Complexity :
- Time Complexity : O(n)
- Space Complexity : O(1)
Method 2 : Code in C++
Run
#include<bits/stdc++.h>
using namespace std;
int main(){
int arr[] = {10, 20, 30, 40, 50};
int n = sizeof(arr)/sizeof(arr[0]);
int start = 0, end = n-1;
while(start < end){
swap(arr[start++], arr[end--]);
}
for(int i=0; i<n; i++)
cout << arr[i] << " ";
}
Output
50 40 30 20 10
Method 3 (Recursive):
- Take variables, start = 0 and end = len – 1
- Function gets called as reverseRecursive(arr, 0, len-1);
- In each recursive iteration swap arr[start] & arr[end]
- Make further recursive calls as reverseRecursive(arr, start + 1, end – 1);
- return when (start >= end)
- Print the array
Time and Space Complexity :
- Time – Complexity : O(n)
- Space-Complexity : O(n), require stack to store the recursive calls.
Method 3 : Code in C++
Run
#include<bits/stdc++.h>
using namespace std;
void reverseRecursive(int arr[], int start, int end)
{
if (start >= end)
return;
int temp = arr[start];
arr[start] = arr[end];
arr[end] = temp;
// recursive call to swap arr[start+1] & arr[end-1]
reverseRecursive(arr, start + 1, end - 1);
}
int main(){
int arr[] = {10, 20, 30, 40, 50};
int n = sizeof(arr)/sizeof(arr[0]);
reverseRecursive(arr, 0, n-1);
for(int i=0; i<n; i++)
cout<<arr[i]<<" ";
}Output
50 40 30 20 10
Method 4 :
In this method we will use inbuilt reverse function to reverse the array.
- reverse() is a predefined function in header file algorithm.
- It reverses the order of the elements in the range [first, last) of any container.
Time and Space Complexity :
- Time – Complexity : O(n)
- Space-Complexity : O(1)
Method 4 : Code in C++
Run
#include<bits/stdc++.h>
using namespace std;
int main(){
int arr[] = {10, 20, 30, 40, 50};
int n = sizeof(arr)/sizeof(arr[0]);
reverse(arr, arr+n);
for(int i=0; i<n; i++)
cout<<arr[i]<<" ";
}
Output
50 40 30 20 10
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#include
using namespace std;
int main()
{
int n;
cin>>n;
int arr[n];
for(int i=0;i>arr[i];
}
cout<<endl;
int s=0;
int e=n-1;
while(s<e)
{
swap(arr[s],arr[e]);
s++;
e–;
}
for(int i=0;i<n;i++)
{
cout<<arr[i]<<" "<<endl;
}
}
#include
using namespace std;
int rev(int* a,int N)
{
int i,j=N-1,temp;
for(i=0;i<j;i++,j–)
{
temp=a[i];
a[i]=a[j];
a[j]=temp;
}
cout<<"reverse array: ";
for(i=0;i<N;i++)
cout<<" "<<a[i];
return 1;
}
int main()
{
int a[20],n,i;
cout<>n;
cout<<"Enter elements: ";
for(i=0;i>a[i];
rev(a,n);
return 0;
}
#include
using namespace std;
int main(){
int n,temp=0;
cin >> n;
int a[n-1];
for(int i=0;i> a[i];
}
int l=n;
for(int i=1;i<=n/2;i++){
temp=a[i-1];
a[i-1]=a[l-1];
a[l-1]=temp;
l–;
}
for(int i=0;i<n;i++){
cout << a[i];
}
}
#include
using namespace std;
int main()
{
int n;
cin >> n;
int arr[n];
int i;
for(i = 0; i > arr[i];
}
cout <= 0; i–)
{
cout << arr[i] <<" ";
}
cout << endl;
return 0;
}