Online Bin Packing with Per-Bin Maximum Delay

Abstract

We study online bin packing with per-bin maximum delay: each sealed bin incurs a unit opening cost plus the longest waiting time among its items. Offline, this becomes a temporal-span packing objective. We prove strong NP-hardness and rule out absolute approximation factors below three halves unless P equals NP. We complement these barriers with a polynomial constant-factor approximation, exact algorithms for several special cases, and an AFPTAS for the fixed-length weighted endpoint subproblem. For adversarial online inputs, we give an efficient randomized algorithm in the ideal random-real model with expected competitive ratio about 2.418 against an oblivious adversary, together with deterministic and randomized lower bounds. Its analysis couples Next-Fit fragmentation to a negative credit generated by silence clusters. Both frontiers are solved exactly when capacity is nonbinding. We also obtain an exact stochastic benchmark for Poisson arrivals when every item has half the bin capacity: we characterize the offline rate, identify an optimal causal policy, and show that two natural asymptotic ratio notions agree and are bounded by four thirds.