Concepts4

NP-completeness classifies decision problems that are both in NP and as hard as any problem in NP via polynomial-time reductions.

Complexity theory classifies problems by the resources required to solve or verify them, such as time and memory.

Meet-in-the-middle splits a hard exponential search into two halves, enumerates each half, and then combines results efficiently.

Knapsack problems ask how to pick items under a weight (or cost) limit to maximize value or to check if a target sum is reachable.