Search engines and how they find information in Intro to Computing - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

How does a search engine find web pages?

Imagine a search engine as a librarian who needs to find books in a huge library. Which step below best describes how the search engine finds web pages?

A It only searches pages stored on the user's computer.

B It waits for users to send web pages directly to it.

C It guesses web pages based on popular topics without visiting them.

D It uses a program called a crawler to visit web pages and collect information about them.

💡 Hint

Think about how a librarian collects books to organize them.

Search engines use crawlers (also called spiders) to visit and read web pages. This is like a librarian walking through the library to find and catalog books.

❓ trace

intermediate

What does the crawler find on a web page?

Look at the simplified flowchart below showing a crawler visiting a web page:

Start -> Visit URL -> Read page content -> Extract links -> Store data -> End

What information does the crawler collect to help the search engine?

A Only the images on the page.

B The text on the page and the links to other pages.

C The user's personal data on the page.

D The color scheme of the page.

💡 Hint

Think about what helps the search engine find and connect pages.

The crawler reads the text to understand the page's content and extracts links to find more pages to visit.

❓ Comparison

advanced

Comparing indexing and crawling

Which statement correctly compares the roles of crawling and indexing in search engines?

A Crawling finds and reads pages; indexing organizes the information for fast searching.

B Indexing finds pages; crawling organizes the information.

C Both crawling and indexing do the same job of finding pages.

D Neither crawling nor indexing is used by search engines.

💡 Hint

Think of crawling as collecting books and indexing as making a catalog.

Crawling is the process of visiting and reading pages. Indexing is storing and organizing the collected information so the search engine can quickly find relevant pages.

❓ identification

advanced

Identify the error in this crawler behavior

A crawler visits pages but never follows links to new pages. What problem will this cause?

A The crawler will collect personal user data accidentally.

B The crawler will find too many pages and slow down the search engine.

C The search engine will only know about the first pages visited and miss many others.

D The crawler will index pages twice causing duplicates.

💡 Hint

Think about how the crawler discovers new pages.

If the crawler does not follow links, it cannot discover new pages beyond the starting points, so the search engine's index will be incomplete.

🚀 Application

expert

Predict the output of a simplified crawler simulation

Given this simplified crawler code simulation:

pages = {"A": ["B", "C"], "B": ["C"], "C": ["A"]}
crawled = set()
def crawl(page):
    if page not in crawled:
        crawled.add(page)
        for link in pages.get(page, []):
            crawl(link)
crawl("A")
print(sorted(crawled))

What will be printed?

Intro to Computing

pages = {"A": ["B", "C"], "B": ["C"], "C": ["A"]}
crawled = set()
def crawl(page):
    if page not in crawled:
        crawled.add(page)
        for link in pages.get(page, []):
            crawl(link)
crawl("A")
print(sorted(crawled))

A ["A", "B", "C"]

B ["A", "B"]

C ["B", "C"]

D []

💡 Hint

Trace the calls and see which pages get added to the set.

The crawler starts at "A", adds it, then visits "B" and "C". "B" links to "C" which is already added, and "C" links back to "A" which is also added. So all three pages are crawled.

Practice

1. What is the main role of a search engine crawler?

easy

A. To display search results to users

B. To organize information into categories

C. To visit web pages and collect information

D. To delete outdated web pages from the internet

Solution

1. Step 1: Understand the crawler's function

   A crawler is a program that visits many web pages to gather data.

2. Step 2: Differentiate from other parts

   Unlike indexers or searchers, crawlers focus on collecting information, not organizing or displaying it.

3. Final Answer:

   To visit web pages and collect information -> Option C

4. Quick Check:

   Crawler = Collects data [OK]

Hint: Crawlers collect data by visiting pages [OK]

Common Mistakes:

• Confusing crawlers with indexers
• Thinking crawlers display results
• Assuming crawlers delete pages

2. Which of the following is the correct order of steps a search engine uses to find information?

easy

A. Indexing -> Crawling -> Searching

B. Searching -> Crawling -> Indexing

C. Searching -> Indexing -> Crawling

D. Crawling -> Indexing -> Searching

Solution

1. Step 1: Recall the search engine process

   First, the crawler visits pages (Crawling), then the data is organized (Indexing), and finally results are shown (Searching).

2. Step 2: Match the correct sequence

   Only Crawling -> Indexing -> Searching lists the steps in the correct order.

3. Final Answer:

   Crawling -> Indexing -> Searching -> Option D

4. Quick Check:

   Process order = Crawling, Indexing, Searching [OK]

Hint: Remember: Crawl first, then index, then search [OK]

Common Mistakes:

• Mixing up the order of steps
• Thinking searching happens before indexing
• Assuming indexing happens before crawling

3. Consider this simplified flowchart of a search engine process:



What happens immediately after the search query is received?

medium

A. The search engine shows the results

B. The search engine indexes the data

C. The search engine crawls new web pages

D. The search engine deletes old data

Solution

1. Step 1: Analyze the flowchart sequence

   The flowchart shows the steps: Crawl -> Index -> Search Query -> Show Results.

2. Step 2: Identify the step after receiving the search query

   After the search query, the next step is to show the results to the user.

3. Final Answer:

   The search engine shows the results -> Option A

4. Quick Check:

   After query = Show results [OK]

Hint: After query input, results are displayed [OK]

Common Mistakes:

• Thinking crawling happens after query
• Confusing indexing with showing results
• Assuming data deletion occurs here

4. A student wrote this description of how search engines work:

"Search engines first show results, then crawl web pages, and finally index the data."

What is wrong with this description?

medium

A. Crawling happens after indexing

B. The order of steps is incorrect

C. Search engines do not index data

D. Search engines delete data before crawling

Solution

1. Step 1: Review the correct order of search engine steps

   The correct order is crawling first, then indexing, and finally showing results.

2. Step 2: Compare with the student's description

   The student says results are shown first, which is incorrect.

3. Final Answer:

   The order of steps is incorrect -> Option B

4. Quick Check:

   Correct order ≠ student's order [OK]

Hint: Remember: Crawl -> Index -> Show results [OK]

Common Mistakes:

• Believing results show before crawling
• Thinking indexing is optional
• Assuming data deletion is part of the main steps

5. Imagine a search engine that only crawls web pages but never indexes the data. What problem would users face when searching?

hard

A. Users would get no search results or irrelevant ones

B. Search results would be slow but accurate

C. The search engine would delete all web pages

D. Users would see only images, not text

Solution

1. Step 1: Understand the role of indexing

   Indexing organizes and stores data so the search engine can quickly find relevant results.

2. Step 2: Consider the effect of missing indexing

   Without indexing, the search engine cannot match queries to relevant pages, so users get no or irrelevant results.

3. Final Answer:

   Users would get no search results or irrelevant ones -> Option A

4. Quick Check:

   No indexing = no relevant results [OK]

Hint: No indexing means no useful search results [OK]

Common Mistakes:

• Thinking results would still be accurate
• Assuming crawling deletes pages
• Believing search shows only images