Search and find operations in Intro to Computing - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a search operation in computing?

A search operation is the process of looking through data to find a specific item or value. It is like looking for a book in a library by checking each shelf until you find the right one.

intermediate

Explain the difference between linear search and binary search.

Linear search checks each item one by one until it finds the target. Binary search works on sorted data by repeatedly dividing the search area in half, quickly narrowing down where the target is.

beginner

What is the main requirement for using binary search?

The data must be sorted in order (like numbers from smallest to largest) before you can use binary search.

intermediate

Why is binary search faster than linear search on large data sets?

Because binary search cuts the search area in half each time, it finds the item much faster than checking every item one by one like linear search.

beginner

What does a find operation return if the item is not found?

It usually returns a special value like -1 or 'not found' to show the item is not in the data.

Which search method checks each item one by one?

A Binary search

B Hash search

C Linear search

D Quick search

Linear search goes through each item in order until it finds the target.

What must be true about data to use binary search?

A Data must be in a list

B Data must be random

C Data must be encrypted

D Data must be sorted

Binary search requires sorted data to work correctly.

If a search does not find the item, what is a common result?

A 0

B -1 or 'not found'

C The first item

D An error message

Returning -1 or 'not found' signals the item is missing.

Which search is generally faster on large sorted lists?

A Binary search

B Linear search

C Random search

D Sequential search

Binary search quickly narrows down the search area by halving it each step.

What is the first step in a linear search?

A Check the first item

B Divide the list in half

C Sort the list

D Jump to the middle item

Linear search starts by checking the first item and moves forward.

Describe how linear search works using a real-life example.

Think about searching through a pile of papers for a specific note.

Explain why binary search is more efficient than linear search on sorted data.

Imagine looking for a word in a dictionary.

Practice

1. What is the main idea behind a linear search in a list?

easy

A. Check each item one by one until the target is found

B. Jump directly to the middle item and check only there

C. Sort the list first before searching

D. Use a map to find the item instantly

Solution

1. Step 1: Understand linear search method

   Linear search means looking at each item in order, one after another.

2. Step 2: Identify the correct description

   Only Check each item one by one until the target is found describes checking items one by one until the target is found.

3. Final Answer:

   Check each item one by one until the target is found -> Option A

4. Quick Check:

   Linear search = check items one by one [OK]

Hint: Linear search checks items in order until found [OK]

Common Mistakes:

• Thinking linear search jumps to middle item
• Confusing linear search with binary search
• Assuming list must be sorted first

2. Which of the following is the correct syntax to find the index of element 5 in a Python list named numbers?

easy

A. numbers.index(5)

B. index(numbers, 5)

C. numbers.find(5)

D. find(numbers, 5)

Solution

1. Step 1: Recall Python list method for finding index

   Python lists use the index() method to find the position of an element.

2. Step 2: Match method to syntax

   Only numbers.index(5) is correct syntax to find element 5's index.

3. Final Answer:

   numbers.index(5) -> Option A

4. Quick Check:

   List method to find index = index() [OK]

Hint: Use list.index(value) to find element position [OK]

Common Mistakes:

• Using find() which is for strings, not lists
• Trying to call index as a standalone function
• Confusing method name with other languages

3. What will be the output of the following Python code?

items = [3, 7, 1, 9, 7]
print(items.index(7))

medium

A. Error

B. 3

C. 4

D. 1

Solution

1. Step 1: Understand list and index method

   The list items contains [3, 7, 1, 9, 7]. The index() method returns the first position of the value.

2. Step 2: Find first occurrence of 7

   7 appears first at position 1 (0-based index).

3. Final Answer:

   1 -> Option D

4. Quick Check:

   First 7 at index 1 [OK]

Hint: index() returns first match position [OK]

Common Mistakes:

• Choosing last occurrence index instead of first
• Confusing value with index
• Expecting error due to duplicate values

4. The following code is intended to find the index of 10 in the list data. What is wrong?

data = [4, 8, 10, 15]
position = data.find(10)
print(position)

medium

A. The list is missing the element 10

B. The list method should be index(), not find()

C. The print statement syntax is incorrect

D. The variable name 'position' is invalid

Solution

1. Step 1: Check method used on list

   Python lists do not have a find() method; they use index() to find element positions.

2. Step 2: Identify correct method

   Replacing find() with index() fixes the error.

3. Final Answer:

   The list method should be index(), not find() -> Option B

4. Quick Check:

   List search method = index() [OK]

Hint: Use index() for lists, find() is for strings [OK]

Common Mistakes:

• Assuming find() works on lists
• Thinking element 10 is missing
• Believing print syntax is wrong

5. You have a list of student names: students = ['Anna', 'Bob', 'Cara', 'Dan', 'Eli']. You want to check if 'Zoe' is in the list and print her position if found, otherwise print -1. Which code snippet correctly does this efficiently?

hard

A. print(students.find('Zoe'))

B. for i in range(len(students)):
if students[i] == 'Zoe':
print(i)
break

C. print(students.index('Zoe') if 'Zoe' in students else -1)

D. if 'Zoe' in students:
print(students.index('Zoe'))

Solution

1. Step 1: Understand the goal

   We want to check if 'Zoe' is in the list ('Zoe' not present) and print her position if found, else -1, efficiently without errors.

2. Step 2: Analyze options for correctness and efficiency

   print(students.index('Zoe') if 'Zoe' in students else -1) uses conditional expression to print index or -1 safely and efficiently. for i in range(len(students)): if students[i] == 'Zoe': print(i) break loops but prints nothing if not found. print(students.find('Zoe')) uses invalid find() for lists. if 'Zoe' in students: print(students.index('Zoe')) prints only if found, nothing otherwise.

3. Final Answer:

   print(students.index('Zoe') if 'Zoe' in students else -1) -> Option C

4. Quick Check:

   Safe check and index with conditional expression [OK]

Hint: Use conditional index with membership check to avoid errors [OK]

Common Mistakes:

• Using find() on list causing error
• Not printing -1 when element missing
• Writing longer loops instead of simple condition