4. (6 marks) (Adapted from Dasgupta et al., Question 5.15) Suppose that we use the Huffman encoding algorithm to obtain an encoding for the alphabet {a,b,c} with frequencies fa, fb, fc. In each of the following cases, either give an example of frequencies (fa, fb, fc) that would yield the specified code, or explain WHY the code cannot possibly be obtained (no matter what the frequencies are).

(a) {0, 1, 11}

(b) {01, 10, 11}

(c) {00, 01, 1}