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A comprehensive guide to the Hackerrank Day 8 challenge using `Dictionaries and Maps` in Python. Learn how to build a phone book and query it efficiently.
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Solving the Hackerrank Day 8: Dictionaries and Maps Challenge in Python

The world of programming often presents us with unique challenges, and one such task in Python is the Hackerrank Day 8 challenge, centered around the Dictionaries and Maps data structure. This problem not only develops your understanding of dictionaries but also sharpens your skills in data lookups.

In this guide, we will break down the problem, construct the solution, and address a common issue encountered by many, including our very own query about missing outputs.

Understanding the Problem

The challenge arises as follows:

You are required to:

Build a phone book that maps names to their respective phone numbers.

Accept multiple queries, each having a name, and return the associated phone number or indicate if the name does not exist.

Input Format

The first input line specifies the number of entries, n.

The next n lines include a friend's name and their 8-digit phone number separated by space.

After the entries, an unknown number of queries is provided until no more input is given.

Desired Output Format

For each query, output the corresponding phone number or "Not found" if the name does not exist.

Example Input

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Example Output

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Constructing the Solution

Let’s break down our solution into specific parts.

1. Input and Dictionary Construction

First, we need to read the number of entries into our phone book and create a dictionary to store the name and phone number pairs.

[[See Video to Reveal this Text or Code Snippet]]

2. Handling Queries

Next, we will handle queries. However, here’s where many run into problems. An issue arises from how we read inputs for queries. It is essential to avoid calling input() multiple times within the same block.

The Common Mistake

Many mistakenly use input() twice in their while loop to read the input and check for an empty line.

[[See Video to Reveal this Text or Code Snippet]]

The Correct Approach

Instead, we should read the input once per loop iteration, store it, and check if it indicates the end of input:

[[See Video to Reveal this Text or Code Snippet]]

3. Outputting Results

Lastly, we loop through our queries list and check if each name exists in the phonebook:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

In summary, the Hackerrank Day 8 challenge provides an excellent opportunity to work with dictionaries in Python. By carefully managing your input methods and understanding the dictionary syntax, you can effectively create a simple, functional phone book application.

By following the structured approach outlined in this post, you should now have a deeper understanding of solving similar programming challenges and avoid the common pitfalls associated with handling user input.

Happy coding!