kotlin coding test course, finding the Kth number in an array

This article will deal with the problem of finding the K-th number in an array. This problem is one of the types that frequently appears in coding tests and requires an understanding of array sorting and indexing. Let’s learn how to utilize Kotlin’s useful features and implement optimized algorithms in the process of solving this problem.

Problem Description

Given an integer array arr and an integer K, write a function that returns the K-th number after sorting the array in ascending order. The array indices start from 0, and K is between 1 and the size of the array.

Input

  • First line: N (the size of the array)
  • Second line: An array consisting of N integers
  • Third line: K (the position of the K-th number to find)

Output

After sorting the array in ascending order, output the K-th number.

Example

Input
5
3 1 2 5 4
2

Output
2

Problem Analysis

To solve the problem, the following steps must be taken:

  1. Receive the input and store the array and K values.
  2. Sort the array in ascending order.
  3. Access the K-1 index to find the K-th number.
  4. Output the result.

Implementing in Kotlin

Kotlin is a modern language that supports both functional programming and object-oriented programming simultaneously. Therefore, it allows writing very concise and intuitive code when solving this problem.

Code Implementation


fun findKthNumber(arr: IntArray, k: Int): Int {
    // Sort the array in ascending order
    val sortedArray = arr.sortedArray()
    // Return the K-th number (k-1 index)
    return sortedArray[k - 1]
}

fun main() {
    // Set initial values
    val n = 5
    val inputArray = intArrayOf(3, 1, 2, 5, 4)
    val k = 2

    // Find the K-th number
    val result = findKthNumber(inputArray, k)
    println(result)
}

Code Explanation

The above code consists of the following parts:

  1. findKthNumber function: This function takes an integer array and K as input and returns the K-th number. It sorts the array in ascending order and looks for the result using the K-1 index.
  2. sortedArray: Uses Kotlin’s sortedArray method to easily sort the array.
  3. main function: The starting point of the program, it sets the input values and calls the findKthNumber function to output the result.

Time Complexity Analysis

The time complexity of this problem is proportional to the time required to sort the array. The sorting algorithm typically requires O(N log N) time, and the process of finding the K-th number takes O(1). Therefore, the overall time complexity is O(N log N).

Conclusion

In this article, we discussed the problem of finding the K-th number in an array and examined a simple implementation method using Kotlin. Since problems like this will frequently appear in future coding test preparations, it is important to enhance understanding of algorithms and improve coding skills through repetitive practice.

Additionally, when solving algorithm problems, one should pay attention to the following points:

  • Understand and follow the conditions of the problem accurately.
  • Consider optimizing time complexity by selecting efficient algorithms.
  • Perform sufficient testing for all possible cases to prevent bugs.

In the next course, we will address other types of algorithm problems. Please stay tuned!