7.使用LZ77算法对一个序列进行编码。给定C(a)=1,C(/b)=2,C(r)=3,C(t)=5。对一下三元组序列进行编码：
<0,0,3> <0,0,1> <0,0,4> <2,8,2> <3,1,2> <0,0,3> <6,4,4> <9,5,4>
假定窗口的大小为20，现行缓冲区的大小为10。对解码所得到的序列进行编码，确保得到相同的三元组序列。
解：
根据题意知：窗口大小为20，前向缓冲区大小为10，搜索窗口大小10。
C(a) = 1, C( _空格) = 2, C(r) = 3, C(t) = 4
说明2的编码表示空格用下划线"_"
下面编码过程中，最后面含有空格的用下划线"_"表示。
| 输入 | 输出 |
| <0, 0, 3> | r |
| <0, 0, 1> | ra |
| <0, 0, 4> | rat |
| <2, 8, 2> | ratatatatat |
| <3, 1, 2> | ratatatatat a_ |
| <0, 0, 3> | ratatatatat a r |
| <6, 4, 4> | ratatatatat a rat at_ |
| <9, 5, 4> | ratatatatat a rat at a rat |
编码过程：输入序列：ratatatatat a rat at a rat
接下来继续编码：
| 输入 | 输出 |
| ||ratatatatat a rat at a rat | <0, 0, 3> |
| |r|atatatatat a rat at a rat | <0, 0, 1> |
| |ra|tatatatat a rat at a rat | <0, 0, 4> |
| |rat|atatatat a rat at a rat | <2, 8, 2> |
| ra|tatatatat |a rat at a rat | <3, 1, 2> |
| rata|tatatat a |rat at a rat | <0, 0, 3> |
| ratat|atatat a r|at at a rat | <6, 4, 4> |
| ratatatata|t a rat at| a rat | <9, 5, 4> |
根据这2个过程得出：编码输出的三元组与解码输入的三元组完全一样。
8.给定一下初始词典和接收序列，构建一个LZW词典，并对所发送的序列进行编码。
接收序列：4,5,3,1,2,8,2,7,9,7,4
初始字典：
| 索引 | 项 |
| 1 | S |
| 2 | |
| 3 | I |
| 4 | T |
| 5 | H |
解：
对接收序列：4,5,3,1,2,8,2,7,9,7,4进行编码，得到如下结果：
说明2的编码表示空格用下划线"_"
(1）输入4,5,3,1,2,8,2,7,9,7,4
| 索引 | 条目 |
| 1 | S |
| 2 | _(空格) |
| 3 | I |
| 4 | T |
| 5 | H |
该数解码的序列为：T
(2）输入4,5,3,1,2,8,2,7,9,7,4
| 索引 | 条目 |
| 1 | S |
| 2 | (空格) |
| 3 | I |
| 4 | T |
| 5 | H |
该数解码的序列为：TH
(3）输入4,5,3,1,2,8,2,7,9,7,4
| 索引 | 条目 |
| 1 | S |
| 2 | _(空格) |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
该数解码的序列为：THI
(4）输入4,5,3,1,2,8,2,7,9,7,4
| 索引 | 条目 |
| 1 | S |
| 2 | _ (空格) |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
| 7 | HI |
该数解码的序列为：THIS
(5）输入4,5,3,1,2,8,2,7,9,7,4
| 索引 | 条目 |
| 1 | S |
| 2 | _ (空格) |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
| 7 | HI |
| 8 | IS |
该数解码的序列为：THIS_
(6）输入4,5,3,1,2,8,2,7,9,7,4
| 索引 | 条目 |
| 1 | S |
| 2 | _ (空格) |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
| 7 | HI |
| 8 | IS |
| 9 | S_ |
该数解码的序列为：THIS IS
(7）输入4,5,3,1,2,8,2,7,9,7,4
| 索引 | 条目 |
| 1 | S |
| 2 | _ (空格) |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
| 7 | HI |
| 8 | IS |
| 9 | S_ |
| 10 | _I |
该数解码的序列为：THIS IS_
（8）输入4,5,3,1,2,8,2,7,9,7,4
| 索引 | 条目 |
| 1 | S |
| 2 | _ (空格) |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
| 7 | HI |
| 8 | IS |
| 9 | S_ |
| 10 | _I |
| 11 | IS_ |
该数解码的序列为：THIS IS HI
(9）输入4,5,3,1,2,8,2,7,9,7,4
| 索引 | 条目 |
| 1 | S |
| 2 | _ (空格) |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
| 7 | HI |
| 8 | IS |
| 9 | S_ |
| 10 | _I |
| 11 | IS_ |
| 12 | _H |
该数解码的序列为：THIS IS HIS_
（10）输入4,5,3,1,2,8,2,7,9,7,4
| 索引 | 条目 |
| 1 | S |
| 2 | _ (空格) |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
| 7 | HI |
| 8 | IS |
| 9 | S_ |
| 10 | _I |
| 11 | IS_ |
| 12 | _H |
| 13 | HIS |
该数解码的序列为：THIS IS HIS HI
(11）输入4,5,3,1,2,8,2,7,9,7,4
| 索引 | 条目 |
| 1 | S |
| 2 | _ (空格) |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
| 7 | HI |
| 8 | IS |
| 9 | S_ |
| 10 | _I |
| 11 | IS_ |
| 12 | _H |
| 13 | HIS |
| 14 | S_H |
该数解码的序列为：THIS IS HIS HIT
最终的解码的序列为THIS IS HIS HIT