On the convex hull of Huffman trees
FREE-DOWNLOAD [PDF] VH Nguyen, TH Nguyen… – Electronic Notes in Discrete …, 2010
It was developed by David A. Huffman  in 1952 and produces prefix- free, variable-length
code words based on the frequency of each character. Huffman gives a greedy algorithm
constructing an optimal tree in O(n log n) time (in term of number of letters).