Hello Everyone,
Given an array, reverse every sub-array formed by consecutive k elements.
Examples:
Input:
arr = [1, 2, 3, 4, 5, 6, 7, 8, 9]
k = 3
Output:
[3, 2, 1, 6, 5, 4, 9, 8, 7]Input:
arr = [1, 2, 3, 4, 5, 6, 7, 8]
k = 5
Output:
[5, 4, 3, 2, 1, 8, 7, 6]Input:
arr = [1, 2, 3, 4, 5, 6]
k = 1
Output:
[1, 2, 3, 4, 5, 6]Input:
arr = [1, 2, 3, 4, 5, 6, 7, 8]
k = 10
Output:
[8, 7, 6, 5, 4, 3, 2, 1]
Approach : Consider every sub-array of size k starting from the beginning of the array and reverse it. We need to handle some special cases. If k is not multiple of n where n is the size of the array, for the last group we will have less than k elements left, we need to reverse all remaining elements. If k = 1 , the array should remain unchanged. If k >= n, we reverse all elements present in the array.
Below is the implementation of the above approach:
// C++ program to reverse every sub-array formed by
// consecutive k elements
#include <iostream>
using namespace std;
// Function to reverse every sub-array formed by
// consecutive k elements
void reverse( int arr[], int n, int k)
{
for ( int i = 0; i < n; i += k)
{
int left = i;
// to handle case when k is not multiple of n
int right = min(i + k - 1, n - 1);
// reverse the sub-array [left, right]
while (left < right)
swap(arr[left++], arr[right--]);
}
}
// Driver code
int main()
{
int arr[] = {1, 2, 3, 4, 5, 6, 7, 8};
int k = 3;
int n = sizeof (arr) / sizeof (arr[0]);
reverse(arr, n, k);
for ( int i = 0; i < n; i++)
cout << arr[i] << " " ;
return 0;
}
Output:
3 2 1 6 5 4 8 7
Time complexity of above solution is O(n).
Auxiliary space used by the program is O(1).