Before revision:  We first considered the case when the number of bins is a constant . Previously a randomized approximation algorithm can obtain approximation ratio (1 - 1/e-\epsilon)  based on the involved continuous greedy technique.
After revision:  We first considered the case when the number of bins is a constant and provide a simple combinatorial deterministic algorithm with an optimal (1-1/e) ratio. Previously, a randomized approximation algorithm can obtain approximation ratio (1 - 1/e-\epsilon) based on the involved continuous greedy technique.