A new technique for efficient encoding of LDPC codes based on the known concept of Approximate Lower Triangulation (ALT) is introduced. The greedy permutation algorithm is presented to transform parity-check matrices into an Approximate Lower Triangular (ALT) form with minimum “Gap”. A large girth, which is known to guarantee good decoding performance, is shown (for a fixed column-weight of the parity-check matrix of the code) to result in a large gap to linear encoding, which demonstrates a fundamental trade-off between complexity and decoding performance.