Time-domain Wavelength Interleaved Networking (TWIN) is a new optical network architecture which achieves a good balance between scheduling flexibility and deployment cost. In this paper, we solve the wavelength assignment problem for TWIN networks using topology sharing approach. We show that determining the wavelength assignment that use the minimum number of wavelengths is a NP-Complete problem. Four greedy heuristics are presented to compute the approximated solution within reasonable time. The evaluation results show that performing sorting on destination trees and wavelengths improves the assignment results, especially under low traffic loads. However, performing sorting brings some extra overheads to the sort heuristics' running time, but overall computation costs are still acceptable.