Prefix Sum and Sliding Window 07

Given an array of integers Arr of size N and a number K. Return the maximum sum of a subarray of size K.

Problem link :- click here

Code

import java.util.Scanner;

//	MAX SUM SUBARRAY OF SIZE K

public class Prefix_sum__Sliding_window_07
{
	
	static int maxSumOfSubarrayOfSizeK(int arr[], int k)
	{
		if(k > arr.length)
			return -1;
		
		//	SLIDING WINDOW
		/*
		 	arr = {100, 200, 300, 100}	k = 2
		 	
		 	step1: - add the values of first k elements to `sum` and update `maxSum`.
		 	step2: - until last element of the `arr`	( i=k  to  i=n)
		 		    i) subtract the value of leftmost element which is not yet subtracted 
		 		       from `sum`.
		 		    ii) add the value of the present element in the iteration. i.e., `i`.
		 		    iii) update the `maxSum`.
		 	
		 	sum = arr[0] + arr[2]
		 	sum = 100 + 200
		 		 = 300
		 	maxSum = 300 
		 	
		 	sum = sum - arr[0]		subtract
		 		 = 300 - 100
		 		 = 200
		 	sum = sum + arr[2]		add
		 		 = 200 + 300
		 		 = 500
		 	maxSum = 500
		 	
		 	sum = sum - arr[1]		subtract
		 		 = 500 - 200
		 		 = 300
		 	sum = sum + arr[3]		add
		 		 = 300 + 100
		 		 = 400
		 	maxSum = 500
		 */
		
		int maxSum = 0;
		int sum = 0;
		
		//step1: -
		for(int i=0; i<k; i++)
			sum += arr[i];
		
		if(sum > maxSum)
			maxSum = sum;
		
		//step2: -
		for(int i=k; i<arr.length; i++)
		{
			sum -= arr[i-k];
			sum += arr[i];
			
			if(sum > maxSum)
				maxSum = sum;
		}
		
		return maxSum;
	}

	public static void main(String[] args)
	{
		Scanner s = new Scanner(System.in);
		
		//	Taking size of array and array as input from the user
		System.out.print("Enter the size of the array : ");
		int n = s.nextInt();
		
		int[] arr = new int[n];
		System.out.println("Enter the array elements : ");
		for(int i=0; i<n; i++)
			arr[i] = s.nextInt();
		
		System.out.print("Enter the value of k : ");
		int k = s.nextInt();
		
		int maxSum = maxSumOfSubarrayOfSizeK(arr, k);
		System.out.println(maxSum);

		s.close();
	}

}