Today, I am going to write a blog post for job seekers. This tutorial will emphasize the importance of algorithms and data structures that are essential to effectively solving problems in coding tests, and I will explain how to apply them with specific examples through real problems.
1. The Necessity of Coding Tests
Many modern companies are increasingly assessing candidates’ problem-solving abilities through technical interviews. Therefore, it is important to understand the algorithms and data structures needed in practice and to develop the ability to solve problems based on them.
2. Algorithms and Data Structures: The Cornerstone
An algorithm is a set of methods by which a computer solves problems, and a data structure is a way to effectively store and manage data. These two elements are complementary to each other and are essential for solving the problems in coding tests.
3. Problem Selection: Example of an Algorithm Problem
Problem Description
Problem: Generate a password
Write a program that generates a new password by using at most two characters from the given string only once. The password can include uppercase and lowercase letters, numbers, and special characters, with a length of at least 8 and at most 16 characters.
Input
The first line contains the string to be used to generate the password.
Output
Print possible passwords, dividing them into cases that include and do not include uppercase and lowercase letters, numbers, and special characters.
Example Input
abc123@!
Example Output
abc123@!
abc123!
abc12@!
abc123
The above example shows all possible combinations of valid passwords that can be generated from the given string.
4. Problem-Solving Process
4.1. Problem Analysis
To solve the problem, we first need to analyze the given string to determine which characters are available for use. The length of the password is fixed, and the main goal is to find various combinations based on the usage of each character.
4.2. Algorithm Selection
In this problem, a backtracking algorithm can be used. During the password generation process, characters are selected, and the next character is recursively chosen based on that selection. If the selection does not meet the criteria, it is retracted, and the next character is selected.
4.3. Coding
def generate_password(s, current_password, used_chars, index):
if len(current_password) >= 8 and len(current_password) <= 16:
print(current_password)
for i in range(index, len(s)):
if used_chars[s[i]] < 2:
used_chars[s[i]] += 1
generate_password(s, current_password + s[i], used_chars, i + 1)
used_chars[s[i]] -= 1
s = "abc123@!"
used_chars = {char: 0 for char in s}
generate_password(s, "", used_chars, 0)5. Code Explanation
The code above generates passwords in a recursive manner. Here is an explanation of the main parts of the code:
- generate_password: A recursive function that generates the password. It selects the next character based on the current selected password from the given string.
- used_chars: A dictionary that records how many times each character has been used. This allows for a maximum of two uses of each character.
- Condition: Prints the current password when its length is between 8 and 16 characters.
6. Time Complexity Analysis
The time complexity of this algorithm is O(n^k) in the worst case, where n is the length of the string and k is the length of the password. However, since the length of valid passwords is limited, the speed does not decrease significantly in practice.
7. Testing and Validation
After writing the code, it is important to validate the code against various input values. For example:
- Strings containing a mix of special characters, numbers, and letters
- Strings that are completely impossible to generate passwords from
- Strings containing Korean characters
8. Conclusion
The problem we reviewed today is a common type of question in coding tests, demonstrating the importance of algorithm selection. It is important to develop the ability to solve various problems through the harmony of necessary data structures and algorithms.
9. Additional Learning Resources
If you are looking for additional algorithm problem-solving resources, I recommend the following books and sites:
10. Questions and Feedback
If you have any questions or additional feedback regarding this post, please feel free to let me know in the comments. I hope your journey to prepare for coding tests becomes easier!