Run-length encoding: encoding text
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. What is AAAABBB run-length encoded?
2. How many runs are in the string WWWBBWWWW?
3. Which is the correct run-length encoding of the string CCCCCC?
4. How is a single X on its own written in run-length encoding?
5. Which is the correct encoding of AABCCC?
B
Match the Pairs
Draw a line connecting each item on the left to its match on the right.
| Left column | Right column | |
|---|---|---|
| 1AAAABBB → 4A3B | AOne run of 8 identical characters is written as the count 8 then the letter W | |
| 2WWWWWWWW → 8W | BEach run of identical characters is replaced by a count followed by the character | |
| 3A single character that is not repeated still gets a count of 1 | CThe single B is missing its count. It should be written 1B, so the answer is 2A1B3C. | |
| 4Count the runs first, then write each count followed by its character | DAAABCC → 3A1B2C | |
| 5AAAABBB → A4B3 | EThe character is written before the count. The count must come first, so it should be 4A3B. | |
| 6AABCCC → 2AB3C | FXXYYYZZZZ → 2X3Y4Z |
C
Definitions
4A3B
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
Encode AAAABBB: _A3B
2.
Encode WWWWWWBB: 6W_B
3.
Encode ABBB: _A3B
4.
Encode CCCDD: 3_2D
5.
Encode AABAAA: 2A1B_A
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
Input: AAAABBB
B
Runs: AAAA, BBB
C
Counts: 4 and 3
D
Output: A4B3
Question 2
A
Input: WWWWWB
B
Runs: WWWWW, B
C
Output: 5WB
Question 3
A
Input: CCDDDDE
B
Runs: CC, DDDD, E
C
Counts: 2, 4, 1
D
Output: 2C3D1E
Question 4
A
Input: ZZZZZZ
B
Run length: 5
C
Output: 6Z
Question 5
A
text = AAABCC
B
runs = AAA, B, CC
C
encoded = 3A2B2C
Answer Key
Run-length encoding: encoding text
Section A: Quick Questions
Q1
A — 4A3B
Q2
A — 3 runs
Q3
B — 6C
Q4
A — 1X
Q5
B — 2A1B3C
Section B: Match the Pairs
Q1
AAAABBB → 4A3B → Each run of identical characters is replaced by a count followed by the character
Q2
WWWWWWWW → 8W → One run of 8 identical characters is written as the count 8 then the letter W
Q3
A single character that is not repeated still gets a count of 1 → AAABCC → 3A1B2C
Q4
Count the runs first, then write each count followed by its character → XXYYYZZZZ → 2X3Y4Z
Q5
AAAABBB → A4B3 → The character is written before the count. The count must come first, so it should be 4A3B.
Q6
AABCCC → 2AB3C → The single B is missing its count. It should be written 1B, so the answer is 2A1B3C.
Section C: Definitions
Q1
4A3B — Run-length encoding: each run of identical characters becomes a count then the character, so AAAABBB is written 4A3B. A single character is written 1X.Section D: Fill in the Blanks
Q1
Encode AAAABBB: 4A3BQ2
Encode WWWWWWBB: 6W2BQ3
Encode ABBB: 1A3BQ4
Encode CCCDD: 3C2DQ5
Encode AABAAA: 2A1B3ASection E: Spot the Error
Q1
D — Run-length encoding writes the count first, then the character. The output should be 4A3B, not A4B3.
Q2
C — A single character still needs a count of 1. The lone B must be written 1B, so the output is 5W1B.
Q3
D — The run of D is four letters long, as the Counts line says. It should be 4D, so the output is 2C4D1E.
Q4
B — ZZZZZZ has six Z characters, so the run length is 6, not 5. This matches the output 6Z.
Q5
C — There is only one B in the text, so it should be written 1B. The encoded string should be 3A1B2C.