MaximumSum.java

package collectionz;

//JAVA Code for Find maximum (or minimum) 
//sum of a subarray of size k
import java.util.*;

class MaximumSum {
 
 // Returns maximum sum in a subarray of size k.
 public static int maxSum(int arr[], int n, int k)
 {
     // k must be greater
     if (n < k)
     {
        System.out.println("Invalid");
        return -1;
     }
  
     // Compute sum of first window of size k
     int res = 0;
     for (int i=0; i<k; i++)
        res += arr[i];
  
     // Compute sums of remaining windows by
     // removing first element of previous
     // window and adding last element of 
     // current window.
     int curr_sum = res;
     for (int i=k; i<n; i++)
     {
        curr_sum += arr[i] - arr[i-k];
        res = Math.max(res, curr_sum);
     }
  
     return res;
 }
 
 /* Driver program to test above function */
 public static void main(String[] args) 
 {
     int arr[] = {1, 4, 2, 10, 2, 3, 1, 0, 20};
     int k = 4;
     int n = arr.length;
     System.out.println(maxSum(arr, n, k));
 }
}