C++ program to find maximum of each k sized contiguous subarray

Suppose we have an array with n elements and a value k. We shall have to find maximum value for each of the contiguous subarray of size k.

So, if the input is like arr = [3,4,6,2,8], k = 3, then the output will be The contiguous subarrays of size 3 are [3,4,6], [4,6,2], [6,2,8], so the maximum elements are 6, 6 and 8.

To solve this, we will follow these steps −

• Define one deque Qi of size k
• for initialize i := 0, when i
• while Qi is not empty and arr[i] >= arr[last element of Qi], do:
  • delete last element from Qi
• insert i at the end of Qi

Example

Let us see the following implementation to get better understanding −

#include 
#include 
#include 
using namespace std;
int main(){
   vector arr = {3,4,6,2,8};
   int k = 3;
   deque Qi(k);
   int i;
   for (i = 0; i = arr[Qi.back()])
         Qi.pop_back();

         Qi.push_back(i);
     }
     for ( ; i = arr[Qi.back()])
            Qi.pop_back();
        Qi.push_back(i);
    }
    cout 

Input
{3,4,6,2,8}, 3
Output
6 6 8