Pattern recognition in Intro to Computing - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the next number in the sequence

Look at this number sequence:

2, 4, 8, 16, ...

What is the next number?

A 24

B 20

C 18

D 32

💡 Hint

Each number is multiplied by 2 to get the next.

This sequence doubles each time: 2 × 2 = 4, 4 × 2 = 8, 8 × 2 = 16, so next is 16 × 2 = 32.

❓ trace

intermediate

Trace the pattern in the code output

What does this code print?

Intro to Computing

for i in range(1, 6):
    print(i * '*')

A

1
2
3
4
5

B

*****
****
***
**
*

C

*
**
***
****
*****

D Error: cannot multiply string by int

💡 Hint

Multiplying a string by a number repeats the string.

The loop prints 1 star, then 2 stars, up to 5 stars, each on a new line.

❓ Comparison

advanced

Compare patterns in two sequences

Which sequence follows the same pattern as this one?

3, 6, 12, 24, ...

A 2, 4, 8, 16, 32

B 3, 9, 27, 81, 243

C 5, 10, 15, 20, 25

D 1, 3, 6, 10, 15

💡 Hint

Look for how each number changes to the next.

Both sequences multiply by 2 each time: 3×2=6, 6×2=12, etc. and 2×2=4, 4×2=8, etc.

❓ identification

advanced

Identify the pattern type from a description

A pattern adds the previous two numbers to get the next. Which is this pattern?

A Fibonacci sequence

B Geometric sequence

C Arithmetic sequence

D Prime numbers

💡 Hint

Think about a famous sequence where each number is sum of two before it.

The Fibonacci sequence starts with 0 and 1, then each number is the sum of the two before it.

🚀 Application

expert

Predict the output of a complex pattern code

What is the output of this code?

Intro to Computing

def pattern(n):
    result = []
    for i in range(1, n+1):
        line = ''.join(str(x) for x in range(i, 0, -1))
        result.append(line)
    return '\n'.join(result)

print(pattern(4))

A

1
12
123
1234

B

1
21
321
4321

C

4
43
432
4321

D Error: invalid syntax

💡 Hint

Look at how the inner loop counts down from i to 1.

The code builds lines counting down from i to 1, so line 3 is '321', line 4 is '4321'.

Practice

1. What is the main purpose of pattern recognition in computing?

easy

A. To find repeated or similar parts in data

B. To write long and complex code

C. To slow down program execution

D. To avoid using rules in programs

Solution

1. Step 1: Understand pattern recognition meaning

   Pattern recognition means finding repeated or similar parts in data.

2. Step 2: Identify its purpose in computing

   It helps programs handle many cases with simple rules, making problem solving faster.

3. Final Answer:

   To find repeated or similar parts in data -> Option A

4. Quick Check:

   Pattern recognition = find repeated parts [OK]

Hint: Pattern recognition means spotting repeats or similarities [OK]

Common Mistakes:

• Thinking pattern recognition slows programs
• Believing it makes code more complex
• Confusing it with avoiding rules

2. Which of the following is the correct way to describe a pattern recognition rule in a program?

easy

A. Repeat the same action regardless of data

B. Ignore all data and do nothing

C. If data matches a pattern, then perform an action

D. Write random code without rules

Solution

1. Step 1: Understand pattern recognition rules

   Rules check if data matches a pattern to decide what to do next.

2. Step 2: Match options to this idea

   Only If data matches a pattern, then perform an action says to perform an action if data matches a pattern.

3. Final Answer:

   If data matches a pattern, then perform an action -> Option C

4. Quick Check:

   Rule = if pattern then action [OK]

Hint: Rules act only when data matches patterns [OK]

Common Mistakes:

• Choosing options that ignore data
• Thinking rules always repeat actions
• Confusing randomness with rules

3. Consider this simple pattern recognition code snippet:

data = [2, 4, 6, 8, 10]
result = []
for num in data:
    if num % 4 == 0:
        result.append(num)
print(result)

What will be the output?

medium

A. [2, 4, 6, 8, 10]

B. [4, 8]

C. [2, 6, 10]

D. []

Solution

1. Step 1: Identify the pattern condition

   The code checks if each number is divisible by 4 (num % 4 == 0).

2. Step 2: Check each number in data list

   Numbers divisible by 4 are 4 and 8, so result will be [4, 8].

3. Final Answer:

   [4, 8] -> Option B

4. Quick Check:

   Divisible by 4 = [4, 8] [OK]

Hint: Check divisibility condition for each number [OK]

Common Mistakes:

• Including numbers not divisible by 4
• Ignoring the condition and printing all
• Confusing modulo operator meaning

4. The following code is intended to find all even numbers in a list, but it has a bug:

numbers = [1, 2, 3, 4, 5]
even_nums = []
for n in numbers:
    if n / 2 == 0:
        even_nums.append(n)
print(even_nums)

What is the error and how to fix it?

medium

A. The print statement is missing parentheses

B. The list 'numbers' is empty, so no output

C. The append method is misspelled

D. The condition should use '==' with modulo: 'if n % 2 == 0:'

Solution

1. Step 1: Identify the condition error

   The code uses 'n / 2 == 0' which checks division result equals zero, always false for positive n.

2. Step 2: Correct the condition to check evenness

   Use modulo operator '%' to check remainder: 'if n % 2 == 0:' to find even numbers.

3. Final Answer:

   The condition should use '==' with modulo: 'if n % 2 == 0:' -> Option D

4. Quick Check:

   Even check = n % 2 == 0 [OK]

Hint: Use modulo (%) to check even numbers [OK]

Common Mistakes:

• Using division instead of modulo
• Assuming empty list causes error
• Misspelling method names

5. You have a list of words: words = ['apple', 'banana', 'apricot', 'berry', 'avocado']. You want to create a new list containing only words that start with 'a' using pattern recognition. Which code snippet correctly does this?

hard

A. filtered = [w for w in words if w[0] == 'a']

B. filtered = [w for w in words if w.endswith('a')]

C. filtered = [w for w in words if 'a' in w]

D. filtered = [w for w in words if w[1] == 'a']

Solution

1. Step 1: Understand the pattern to match

   We want words starting with 'a', so check first letter w[0] == 'a'.

2. Step 2: Evaluate each option

   filtered = [w for w in words if w[0] == 'a'] correctly filters words where first letter is 'a'. Others check wrong positions or conditions.

3. Final Answer:

   filtered = [w for w in words if w[0] == 'a'] -> Option A

4. Quick Check:

   Start with 'a' = w[0] == 'a' [OK]

Hint: Check first character with w[0] == 'a' [OK]

Common Mistakes:

• Using endswith instead of startswith
• Checking wrong character index
• Checking if 'a' is anywhere in word