given an array, for each element, find out the total number of elements lesser than it, which appear to the right of it

Question

I had previously posted a question, Given an array, find out the next smaller element for each element now, i was trying to know , if there is any way to find out \"given an ar

Answer 1

Instead of BST, you can use stl map.

Start inserting from right. After inserting an element, find its iterator:

auto i = m.find(element);

Then subtract it from m.end(). That gives you the number of elements in map which are greater than current element.

map m;
for (int i = array.size() - 1; i >= 0; --i) {
  m[array[i]] = true;
  auto iter = m.find(array[i])
  greaterThan[i] = m.end() - iter;
}

Hope it helped.