第四次作业
7、使用LZ77算法对一个序列进行编码。给定C(a)=1，C(p)=2，C(r)=3，C(t)=4。对已下三元组序列进行解码：
<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，先行缓冲区的大小为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。
答： 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( ) = 2, C(r) = 3, C(t) = 4
解码过程如下表：
| 序列 | 输出 |
| <0,0,3> | r |
| <0,0,1> | ra |
| <0,0,4> | rat |
| <2,8,2> | ratatatatatb |
| <3,1,2> | ratatatatatbab |
| <0,0,3> | ratatatatatbabr |
| <6,4,4> | ratatatatatbabratbat |
| <9,5,4> | ratatatatatbabratbatbabrat |
（2）编码：由于窗口的大小为20，先进性缓冲区的大小为10，可得编码缓冲区的大小为10
开始解码序列为：ratatatatatbabratbatbabrat
输入序列为： l ratatatatatbabratbatbabrat 没有与r匹配的项 因此输出三元组为：<0,0,3>
输入序列为：r l atatatatatbabratbatbabrat 没有与a匹配的项 因此输出三元组为：<0,0,1>
输入序列为：ra l tatatatatbabratbatbabrat 没有与t匹配的项 因此输出三元组为：<0,0,4>
输入：4, 5, 3, 1, 2, 8, 2, 7, 9, 7, 4
解码出的序列：T
字典：
| 1 | S |
| 2 | |
| 3 | I |
| 4 | T |
| 5 | H |
输入：4, 5, 3, 1, 2, 8, 2, 7, 9, 7, 4
解码出的序列：TH
字典：
| 1 | S |
| 2 | |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
输入4,5,3,1,2,8,2,7,9,7,4
解码的序列为：THIS
| 1 | 5 |
| 2 | - |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
| 7 | HI |
输入4,5,3,1,2,8,2,7,9,7,4
解码的序列为：THIS_
| 1 | S |
| 2 | - |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
| 7 | HI |
| 8 | IS |
输入4,5,3,1,2,8,2,7,9,7,4
解码的序列为：THIS IS
| 1 | S |
| 2 | - |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
| 7 | HI |
| 8 | IS |
| 9 | S- |
输入4,5,3,1,2,8,2,7,9,7,4
解码的序列为：THIS IS_
| 1 | S |
| 2 | - |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
| 7 | HI |
| 8 | IS |
| 9 | S- |
| 10 | -I |
输入4,5,3,1,2,8,2,7,9,7,4
解码的序列为：THIS IS HI
| 1 | S |
| 2 | - |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
| 7 | HI |
| 8 | IS |
| 9 | S- |
| 10 | -I |
| 11 | IS- |
输入4,5,3,1,2,8,2,7,9,7,4
解码的序列为：THIS IS HIS_
| 1 | S |
| 2 | - |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
| 7 | HI |
| 8 | IS |
| 9 | S- |
| 10 | -I |
| 11 | IS- |
| 12 | -H |
输入4,5,3,1,2,8,2,7,9,7,4
解码的序列为：THIS IS
| 1 | S |
| 2 | - |
| 3 | I |
| 4 | T |
| 5 | H |
| 6 | TH |
| 7 | HI |
| 8 | IS |
| 9 | S- |
| 10 | -I |
| 11 | IS- |
| 12 | -H |
| 13 | HIS |
输入4,5,3,1,2,8,2,7,9,7,4
解码的序列为：THIS IS HIS HIT
| 1 | S |
| 2 | - |
| 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 |
所以解码的序列为THIS IS HIS HIT
