Reverse array in groups

Problem Statement - link #

Given an array arr[] of positive integers of size N. Reverse every sub-array group of size K.

Your Task: You don’t need to read input or print anything. The task is to complete the function reverseInGroups() which takes the array, N and K as input parameters and modifies the array in-place.

Expected Time Complexity: O(N).
Expected Auxiliary Space: O(N).

Examples #

Example 1:

Input:
N = 5, K = 3
arr[] = {1,2,3,4,5}
Output: 3 2 1 5 4
Explanation: First group consists of elements
1, 2, 3. Second group consists of 4,5.

Example 2:

Input:
N = 4, K = 3
arr[] = {5,6,8,9}
Output: 8 6 5 9

Constraints #

• 1 <= N,K <= 10^7
• 1 <= A[i] <= 10^18

Solutions #

class Solution{
public:
    //Function to reverse every sub-array group of size k.
    void reverseInGroups(vector<long long>& arr, int n, int k){
        // code here
        for(int i=0; i<n; i+=k){
            if(i+k < n)
            reverse(arr.begin()+i, arr.begin()+(k+i));
            else
            reverse(arr.begin()+i, arr.end());
        }
    }
};