A low complexity algorithm is proposed to jointly allocate the resources, namely subcarrier assignment and power profiles at the sources and relay nodes for two users decode and forward (DF) relaying scheme using orthogonal frequency division multiple access (OFDMA). The objective is to allocate the resources to maximize the weighted sum rate subject to individual power constraint on each node. We formulate such a problem as subcarrier based resource allocation that seeks joint optimization of subcarrier assignment and power profiles at the source and relay nodes. Using high signal-to-noise- ratio (SNR) approximation, the proposed algorithm splits the subcarriers into two partitions based on channel gains' ordering, where each partition is assigned to one user. The computational complexity of finding the subcarrier assignment that maximizes the weighted sum rate for N subcarriers DF-OFDMA scenario is of O(N). The merits of the proposed algorithm is demonstrated by numerical simulations.