Deque STL Hackerrank Solution in C++

Deque STL Hackerrank Solution in C++. Double-ended queues or Deque(part of C++ STL) are sequence containers with dynamic sizes that can be expanded or contracted on both ends (either its front or its back). The member functions of deque that are mainly used are:

Deque Template:

std::deque<value_type>

Declaration:

deque<int> mydeque; //Creates a double-ended queue of deque of int type

Size

int length = mydeque.size(); //Gives the size of the deque

Push

mydeque.push_back(1); //Pushes element at the end
mydeque.push_front(2); //Pushes element at the beginning

Pop

mydeque.pop_back(); //Pops element from the end
mydeque.pop_front(); //Pops element from the beginning

Empty

mydeque.empty() //Returns a boolean value which tells whether the deque is empty or not

Given a set of arrays of size N and an integer K, you have to find the maximum integer for each and every contiguous subarray of size K for each of the given arrays.

Input Format

The first line of input will contain the number of test cases T. For each test case, you will be given the size of array N and the size of the subarray to be used K. This will be followed by the elements of the array Ai.

Constraints

1 <= T <= 1000
1 <= N <= 10000
1 <= K <= N
1 <= Ai <= 10000, where Ai is the ith element in the array A.

Output Format

For each of the contiguous subarrays of size K of each array, you have to print the maximum integer.

Sample Input

2
5 2
3 4 6 3 4
7 4
3 4 5 8 1 4 10

Sample Output

4 6 6 4
8 8 8 10

Explanation

For the first case, the contiguous subarrays of size 2 are {3,4},{4,6},{6,3} and {3,4}. The 4 maximum elements of the subarray of size 2 are 4 6 6 4.

For the second case, the contiguous subarrays of size 4 are {3,4,5,8},{4,5,8,1},{5,8,1,4} and {8,1,4,10}. The 4 maximum elements of the subarray of size 4 are 8 8 8 10.

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Deque STL Hackerrank Solution in C++

#include <bits/stdc++.h>
#include <deque>
using namespace std;

void printKMax(int arr[], int n, int k)
{
	deque<int> De_que;
	int i;

	for (i = 0; i < k; i++)
	{
		while (!De_que.empty() && arr[i] >= arr[De_que.back()])
		{
			De_que.pop_back();
		}

		De_que.push_back(i);
	}

	for (i = k; i < n; i++)
	{
		cout << arr[De_que.front()] << " ";

		while (!De_que.empty() && De_que.front() <= i - k)
		{
			De_que.pop_front();
		}

		while (!De_que.empty() && arr[i] >= arr[De_que.back()])
		{
			De_que.pop_back();
		}

		De_que.push_back(i);
	}

	cout << arr[De_que.front()] << endl;
}

int main()
{
	int t;
	scanf("%d", &t);
	while (t--)
	{
		int n, k;
		cin >> n >> k;
		int i;
		int *arr = new int[n];
		for (i = 0; i < n; i++)
			cin >> arr[i];
		printKMax(arr, n, k);
	}

	return 0;
}