Concepts2

Double Counting

Double counting is the strategy of counting the same quantity in two different ways to derive an equality or an efficient algorithm.

#double counting#contribution technique#handshake lemma+12

⚙️AlgorithmIntermediate

2D Prefix Sum

A 2D prefix sum (also called an integral image) lets you compute the sum of any axis-aligned sub-rectangle in constant time after O(nm) preprocessing.

#2d prefix sum#summed-area table#integral image+12