给定n个字母（或字）在文档中出现的频率序列X=<x1,x2,…,xn>，求出这n个字母的Huffman编码。为方便起见，以下将频率用字母出现的次数（或称权值）w1,w2,…,wn代替。-Given n letters (or words) in the document the frequency of the sequence X = <x1,x2,…,xn> , Find the n-letter Huffman coding. For convenience, the following letter to the frequency with the number of occurrences (or weights) w1, w2, ..., wn instead.