Python Coding Test Course, Finding the K-th Number

In this course, we will learn about preparing for coding tests using Python through the algorithm problem “Finding the Kth Number.” This problem requires basic sorting and list manipulation, making it useful for practicing relevant basic syntax and algorithm techniques.

Problem Description

The problem is as follows:

n: Number of integers
k: The Kth number to find
arr: A list of n integers

1. Find the k-th number in the list.
2. Note that the numbers are positive integers, and the conditions are 1 ≤ n ≤ 1000, 1 ≤ k ≤ n.
3. The k-th number refers to the number at the k-th position in ascending order.

Example

Assuming the following input values are given:

n = 5
k = 2
arr = [5, 2, 3, 1, 4]

For the above input, the output should be as follows:

The 2nd number is 2.

Problem-Solving Strategy

To solve this problem, you can approach it in the following steps:

  1. Input: Obtain the values of n, k, and arr from the user.
  2. Sort: Sort the list arr in ascending order.
  3. Find Kth Number: Since the indexing of the list starts from 0, extract the value at the index k-1 and output it.

Code Implementation

Now, let’s implement the actual code based on the above-solving strategy.

def find_kth_number(n, k, arr):
    # 1. Sort the list
    arr.sort()
    
    # 2. Find the Kth number
    return arr[k - 1]

# Input
n = int(input("Enter the number of integers: "))
k = int(input("Enter the Kth number to find: "))
arr = list(map(int, input("Enter the list of integers (separated by spaces): ").split()))

# Find the Kth number
kth_number = find_kth_number(n, k, arr)
print(f"The {k}th number is {kth_number}.")

Code Explanation

The above code can be explained in three parts:

  1. Function Definition: The find_kth_number function is defined to take n, k, and arr as parameters. This function returns the k-th number.
  2. Sorting: The list is sorted in ascending order using arr.sort().
  3. Return Result: The k-th number is returned through return arr[k - 1]. Since k is taken as user input, k-1 is used to match the 0-based indexing.

Design Considerations

When solving the problem, there are several factors to consider. It is advisable to think about these points before writing the code:

  • Input Validation: It is essential to check if the values of n and k are given within the specified range.
  • Handling Duplicates: When there are duplicate values, it is good to clarify which number to select among the multiple k-th numbers.
  • Time Complexity: Sorting the arr takes O(n log n) time, so choosing an efficient algorithm is necessary.

Additional Practice Problems

If you have learned the basic algorithm for finding the Kth number through this problem, you can further develop your design skills by solving similar problems. Here are additional practice problems:

  1. Find the k-th smallest number among the numbers from 1 to n in a given list.
  2. Given two sorted lists, find the Kth number in the merged list of the two lists.
  3. Solve the problem of searching for the k-th smallest number in a 2D array.

Conclusion

In this course, we have explored the algorithm problem of Finding the Kth Number using Python. When solving algorithm problems, it is essential to clearly understand the problem, devise a solution strategy, and then implement it in code. Through practice, I hope you encounter various types of problems and improve your skills in solving them.

Thank you.