Replace every element in a circular array by sum of next K elements

// Java program for 
// the above approach
import java.util.*;
class GFG{
    
//reverse array
static Vector<Integer> reverse(Vector<Integer> a) 
{
  int i, n = a.size(), t;
  for (i = 0; i < n / 2; i++) 
  {
    t = a.elementAt(i);
    a.set(i, a.elementAt(n - i - 1));
    a.set(n - i - 1, t);
  }
  return a;
}

// Function to find the sum of next
// or previous k array elements
static Vector<Integer> sumOfKelementsUtil(
       Vector<Integer>a, int x)
{
  // Size of the array
  int n = a.size();

  int count, k, temp;

  // Stores the result
  Vector<Integer> ans = new Vector<>();

  // Iterate the given array
  for (int i = 0; i < n; i++) 
  {
    count = 0;
    k = i + 1;
    temp = 0;

    // Traverse the k elements
    while (count < x) 
    {
      temp += a.elementAt(k % n);
      count++;
      k++;
    }

    // Push the K elements sum
    ans.add(temp);
  }

  // Return the resultant vector
  return ans;
}

// Function that prints the sum of next
// K element for each index in the array
static void sumOfKelements(Vector<Integer> arr,
                           int K)
{
  // Size of the array
  int N = (int)arr.size();

  // Stores the result
  Vector<Integer> ans = new Vector<>();

  // If key is negative,
  // reverse the array
  if (K < 0) 
  {
    K = K * (-1);

    // Reverse the array
    arr =  reverse(arr);

    // Find the resultant vector
    ans = sumOfKelementsUtil(arr, K);

    // Reverse the array again to
    // get the original sequence
    ans = reverse(ans);
  }

  // If K is positive
  else 
  {
    ans = sumOfKelementsUtil(arr, K);
  }

  // Print the answer
  for (int i = 0; i < N; i++) 
  {
    System.out.print(ans.elementAt(i) + " ");
  }
}

// Driver Code
public static void main(String[] args)
{
    // Given array arr[]
    Vector<Integer> arr = new Vector<>();
    arr.add(4);
    arr.add(2);
    arr.add(-5);
    arr.add(11);
    int K = 3;

    // Function Call
    sumOfKelements(arr, K);

}
}

// This code is contributed by gauravrajput1

// Java program for the above approach
import java.io.*;

class GFG {

    // Function to print the
    // required resultant array
    static void sumOfKElements(
        int arr[], int n, int k)
    {

        // Reverse the array
        boolean rev = false;

        if (k < 0) {

            rev = true;
            k *= -1;
            int l = 0, r = n - 1;

            // Traverse the range
            while (l < r) {

                int tmp = arr[l];
                arr[l] = arr[r];
                arr[r] = tmp;
                l++;
                r--;
            }
        }

        // Store prefix sum
        int dp[] = new int[n];
        dp[0] = arr[0];

        // Find the prefix sum
        for (int i = 1; i < n; i++) {

            dp[i] += dp[i - 1] + arr[i];
        }

        // Store the answer
        int ans[] = new int[n];

        // Calculate the answers
        for (int i = 0; i < n; i++) {

            if (i + k < n)
                ans[i] = dp[i + k] - dp[i];
            else {

                // Count of remaining elements
                int x = k - (n - 1 - i);

                // Add the sum of all elements
                // y times
                int y = x / n;

                // Add the remaining elements
                int rem = x % n;

                // Update ans[i]
                ans[i] = dp[n - 1]
                         - dp[i]
                         + y * dp[n - 1]
                         + (rem - 1 >= 0 ? dp[rem - 1] : 0);
            }
        }

        // If array is reversed print
        // ans[] in reverse
        if (rev) {
            for (int i = n - 1; i >= 0; i--) {
                System.out.print(ans[i] + " ");
            }
        }
        else {
            for (int i = 0; i < n; i++) {
                System.out.print(ans[i] + " ");
            }
        }
    }

    // Driver Code
    public static void main(String[] args)
    {
        // Given array arr[]
        int arr[] = { 4, 2, -5, 11 };

        int N = arr.length;

        // Given K
        int K = 3;

        // Function
        sumOfKElements(arr, N, K);
    }
}