You need to update the given array, meaning you have to do all the modifications in the same array without using any data structure. Return the length of the updated array which was the goal

1.Good thing in the question was that the array was sorted. All the duplicate elements will be adjacent to each other.
2. I checked if the current and the next element are equal.
3. If they are...

1. The inorder traversal of a bst returns the nodes in asc order. 
2. To find the k th smallest node, you just perform inorder traversal and store the output in an array. 
3. Then the k th largest node would be the (n-k) th smallest node, where n is the total nodes in the bst

I first explained this approach to the interviewer. He looked pretty convinced with the approach....