Max Visible Pins on Screen

The Pinterest mobile app displays pins in a two-column feed. Each pin is represented by a vertical interval [top, bottom) and a column (“L” or “R”). Given an unsorted list of non-overlapping pins and the vertical size of the screen (screen_len), return the maximum number of pins that can be fully visible at the same time. A pin is fully visible if its entire vertical interval fits inside the screen’s vertical window; the window can be placed anywhere along the y-axis. You may assume pins do not overlap within a column and the list can contain duplicates across columns.