Problem - Rectangle Area II

Given a list of axis-aligned rectangles, find the total area covered (counting overlapping regions only once).

Example: rectangles $[[0,0,2,2], [1,0,2,3], [1,0,3,1]]$ have total area $6$. You're solving the rectangle union problem.

Sweep line with interval tree or segment tree solves it in $O(n \log n)$. Constraints: up to $200$ rectangles, coordinates up to $10^9$.