Hacker rank round for Morgan Stanley.

Round 1

Questions: Given two arrays change and arr that consist of n and m integers respectively, in a single operation, any element of arr[i] can be decremented by 1.

In the ith operation, the element at the index change[i] of arr, i.e., arr[change[i]] can be changed. Assume indexing starts from 1.

Regardless of the value of change[i], in the ith operation, any element can be decremented. If change[i] > 0: If arr[change[i]] = 0, it can be changed to NULL.

Note that it is not necessary to change an element to NULL if it is optimal to do so later. You can choose to do nothing or to decrement any element instead.

Find the minimum number of operations required to change all the elements of the array to NULL or report -1 if it is not possible.

public static int getMinOperations(List<Integer> change, List<Integer> arr) {
    // Write your code here
}

For input change = [1, 0, 1, 3, 2, 1, 0, 3, 1, 1] and arr = [2, 1, 2], the output is 8. One of the possible operations flow can be:

1. Decrementing arr[1] - [1, 1, 2]
2. Decrementing arr[1] - [0, 1, 2]
3. Decrementing arr[2] - [0, 0, 2]
4. Decrementing arr[3] - [0, 0, 1]
5. Change arr[2] as change[5] = 2 - [0, NULL, 1]
6. Change arr[1] as change[6] = 1 - [NULL, NULL, 1]
7. Decrementing change[3] - [NULL, NULL, 0]
8. Change arr[3] as change[8] = 3 - [NULL, NULL, NULL]

For case 2:

List<Integer> change = Arrays.asList(0, 0, 0, 2, 1, 3, 2);
List<Integer> arr = Arrays.asList(1, 3, 2);
System.out.println(getMinOperations(change, arr)); // Output: -1