Concepts3
⚙️AlgorithmAdvanced
CDQ Divide and Conquer
CDQ divide and conquer is an offline technique that splits the timeline (or one coordinate) and lets updates from the left half contribute to queries in the right half.
#cdq divide and conquer#offline algorithm#fenwick tree+11
⚙️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
⚙️AlgorithmIntermediate
Prefix Sum and Difference Array
Prefix sums precompute running totals so any range sum [l, r] can be answered in O(1) time as prefix[r] - prefix[l-1].
#prefix sum#difference array#imos method+12