Problem: Given points in 2D, find the closest pair.
Brute force: Check all pairs. .
D&C approach: Sort points by -coordinate.
Divide: Split into left and right halves by .
Conquer: Recursively find closest pair in each half.
Combine: Check pairs crossing the dividing line within a strip of width (where is the min from both halves).
The strip check: Sort strip points by . For each point, only check the next points (geometry limits candidates).
Time: with careful implementation (can be with optimization).