(40%) Find the shortest encoded bit string of the following source sequence: Source sequence: NCTUNCTUNYCUNCTUNYCU (a) (10%) Calculate the entropy of the source sequence. (b) (10%) Use Huffman coding to encode the string. You first calculate probability distribution, develop a binary tree for it, and perform the encoding. (C) (10%) Use extended Huffman coding to encode the string where k=2. You first calculate probability distribution, develop a binary tree for it, and perform the encoding. (d) (10%) Using arithmetic coding. For this case, you can ignore the termination issue in a decoder, and output the shortest bit string of the first 2 symbols only, while the probability distribution is based on the whole sequence