第四次作业
1、 参考书《数据压缩导论（第4版）》 Page 121
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)=5。对一下三组序列进行解码：
<0,0,3><0,0,1><0,0,4><2,8,2><3,1,2><0,0,3><6,4,4><9,5,4>
假设窗口的大小为20，先行缓冲区的大小为10.对解码所得的序列进行编码，确保得到相同的三元组序列。
解：窗口大小为20，先行缓冲区大小为10。
C(a) = 1, C(p ) = 2, C(r) = 3, C(t) = 4
解码过程：
| 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
| 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> |
编码输出的三元组与解码输入的三元组完全一样。
8、给定以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：4,5,3,1,2,8,7,9,7,4
初始词典：
| 索引 | 项 |
| 1 | S |
| 2 | P |
| 3 | I |
| 4 | T |
| 5 | H |
答案：
接收到的序列：4, 5, 3, 1, 2, 8, 2, 7, 9, 7, 4
输入：4, 5, 3, 1, 2, 8, 2, 7, 9, 7, 4
字典： 解码出的序列：T
|
1 |
S |
|
2 |
|
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3 |
I |
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4 |
T |
|
5 |
H |
输入：4, 5, 3, 1, 2, 8, 2, 7, 9, 7, 4
字典： 解码出的序列：TH
|
1 |
S |
|
2 |
|
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3 |
I |
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4 |
T |
|
5 |
H |
|
6 |
TH |
输入：4, 5, 3, 1, 2, 8, 2, 7, 9, 7, 4
字典： 解码出的序列：THI
|
1 |
S |
|
2 |
|
|
3 |
I |
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4 |
T |
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5 |
H |
|
6 |
TH |
|
7 |
HI |
输入：4, 5, 3, 1, 2, 8, 2, 7, 9, 7, 4
字典： 解码出的序列：THIS
|
1 |
S |
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2 |
|
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3 |
I |
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4 |
T |
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5 |
H |
|
6 |
TH |
|
7 |
HI |
|
8 |
IS |
输入：4, 5, 3, 1, 2, 8, 2, 7, 9, 7, 4
字典： 解码出的序列：THIS
|
1 |
S |
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2 |
|
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3 |
I |
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4 |
T |
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5 |
H |
|
6 |
TH |
|
7 |
HI |
|
8 |
IS |
|
9 |
S |
输入：4, 5, 3, 1, 2, 8, 2, 7, 9, 7, 4
字典： 解码出的序列：THIS IS
|
1 |
S |
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2 |
|
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3 |
I |
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4 |
T |
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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
字典： 解码出的序列：THIS IS
|
1 |
S |
|
2 |
|
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3 |
I |
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4 |
T |
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5 |
H |
|
6 |
TH |
|
7 |
HI |
|
8 |
IS |
|
9 |
S |
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10 |
I |
|
11 |
IS |
输入：4, 5, 3, 1, 2, 8, 2, 7, 9, 7, 4
字典： 解码出的序列：THIS IS HI
|
1 |
S |
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2 |
|
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3 |
I |
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4 |
T |
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5 |
H |
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6 |
TH |
|
7 |
HI |
|
8 |
IS |
|
9 |
S |
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10 |
I |
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11 |
IS |
|
12 |
H |
输入：4, 5, 3, 1, 2, 8, 2, 7, 9, 7, 4
字典： 解码出的序列：THIS IS HIS
|
1 |
S |
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2 |
|
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3 |
I |
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4 |
T |
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5 |
H |
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6 |
TH |
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7 |
HI |
|
8 |
IS |
|
9 |
S |
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10 |
I |
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11 |
IS |
|
12 |
H |
|
13 |
HIS |
输入：4, 5, 3, 1, 2, 8, 2, 7, 9, 7, 4
字典： 解码出的序列：THIS IS HIS HI
|
1 |
S |
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2 |
|
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3 |
I |
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4 |
T |
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5 |
H |
|
6 |
TH |
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7 |
HI |
|
8 |
IS |
|
9 |
S |
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10 |
I |
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11 |
IS |
|
12 |
H |
|
13 |
HIS |
|
14 |
S H |
输入：4, 5, 3, 1, 2, 8, 2, 7, 9, 7, 4
字典： 解码出的序列：THIS IS HIS HIT
|
1 |
S |
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2 |
|
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3 |
I |
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4 |
T |
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5 |
H |
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6 |
TH |
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7 |
HI |
|
8 |
IS |
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9 |
S |
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10 |
I |
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11 |
IS |
|
12 |
H |
|
13 |
HIS |
|
14 |
S H |
|
15 |
HIT |
