Interval overlap counting
Given N intervals + query point, count containing intervals. Segment tree indexed by coordinate. O((N+Q) log N).
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Rectangle union area (Klee)
Sweep vertical line. Segment tree on y-axis tracks 'covered length'. Each event O(log N). Total O(N log N).
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2D range trees
Segment tree of segment trees. O(log² N) queries. Rectangle sum, orthogonal range.
k-d tree comparison
k-d tree: simpler but worst-case O(√N) queries. Range tree: O(log^d N) guaranteed.