1. reduce space(encoding) => reduce computing or
communication time
2. Impossible to compress every files.
.Run length
AAAABBBAABBBBBCDDDQM
.alphabets only =>4A3BAA5BC3DQM
.Mixed =>QDABBBAAQEBCDDDQbM
^ ^4
||
Escape character
Q
.Binary file'0' & '1'
51 bits => No EOL
000000000000000000000000000011111111111111000000000
28 14 9
000000000000000000000000001111111111111111110000000
26 18 7
000000000000000000000001111111111111111111111110000
23 24 4
000000000000000000000011111111111111111111111111000
22 26 3
000000000000000000001111111111111111111111111111110
20 30 1
000000000000000000011111110000000000000000001111111
19 7 18 7
000000000000000000011111000000000000000000000011111
19 5 22 5
000000000000000000011100000000000000000000000000111
19 3 26 3
000000000000000000011100000000000000000000000000111
19 3 26 3
000000000000000000011100000000000000000000000000111
19 3 26 3
000000000000000000011100000000000000000000000000111
19 3 26 3
000000000000000000001111000000000000000000000001110
20 4 23 3 1
000000000000000000000011100000000000000000000111000
22 3 20 3 3
011111111111111111111111111111111111111111111111111
1 50
011111111111111111111111111111111111111111111111111
1 50
011111111111111111111111111111111111111111111111111
1 50
011111111111111111111111111111111111111111111111111
1 50
011111111111111111111111111111111111111111111111111
1 50
011000000000000000000000000000000000000000000000011
1 2 46 2
.Huffman Coding
.encode frequent character with shorter string
count [30] = 21
dad [18] = -30
dad [34] = 30
.Prefix code ¡Gno sequence is a prefix
of another
.Optimun prefix code ¡Gshortest encoded
string
Example of non-preprefix code
A : 1 0
B : 0 1 1
C : 0 1 1 1 0
0 1 1 1 0 = B A ?
C ?