In this post we will discuss a simple problem on Arrays. Given an array of numbers, how do we reverse it efficiently?
Here is the simple and effective approach. We start with one index pointing to the start, and another index pointing to the end of the array. We swap the two elements at these indices, increment left index, and decrement right index. We continue this procedure until both indices meet each other. Then we stop. At the end, the array is reversed.
For example, let us consider the array with 5 elements, Here is how it works
Array: [1 2 3 4 5] – swap
 
left right
[5 2 3 4 1] – swap
 
left right
[5 4 3 2 1] – stop

left
right
#include <iostream>
#include <string>
using namespace std;
void swap( int &a, int &b)
{
int temp = a;
a = b;
b = temp;
}
//function to reverse the array
void reverseArray(int *array, int n)
{
int low = 0; //initialize low to first element
int high = n1; //initialize high
while( low < high ) //until both ends meet
{
swap( array[low], array[high] ); //swap the elements
low++; //increment left
high;//decrement right
}
}
void printArray( int *array,int n)
{
for(int i = 0 ; i < n;i++ )
{
cout<<array[i]<<" ";
}
cout<<endl;
}
int main()
{
int n;
cin>>n;
int* array = new int[n];
int i;
for( i = 0 ; i < n ; i++)
{
cin>>array[i];
}
reverseArray( array, n);
printArray( array, n);
return 0;
}