Huffman codes compress data very effectively: savings of 20% to 90% are typical, depending on the characteristics of the data being compressed.
功能：
huffman 编码能有效的压缩数据。
如何解决：
Huffman’s greedy algorithm uses a table giving how often each character occurs (i.e., its frequency) to build up an optimal way of representing each character as a binary string.
we interpret the binary codeword for a character as the simple path from the root to that character ,where 0 means go to the left child and 1 means go to the right child .
we interpret the binary codeword
for a character as the simple path from the root to that character ,where 0 means go to the left child and 1 means go to the right child .
Note that these are not binary search trees, since the leaves need not appear in sorted order and internal nodes do not contain character keys.
an optimal code for a file is always represented by a fully binary tree ,in which every nonleaf has two children .
the tree for an optimal prefix code has exactly |C| leaves ,one for each letter of the alphabet ,ash exactly |c|-1interanl nodes .
what is the meaning
？
when we merge two objects ,the result is a new object whose frequency is the sum of the frequencies of the two object that were merged .