Category: Kotlin coding test

Problem Description

The goal of this problem is to implement an algorithm that sorts given numbers in ascending order. Before outputting the sorted result, read the integers provided as input, remove any duplicate integers, and then output only the sorted result.

Problem Input

            The first line contains the number of integers N. (1 ≤ N ≤ 1,000,000)
            The second line contains N integers, which will be between -1,000,000 and 1,000,000.
            

Problem Output

            Output the sorted numbers, one per line in increasing order. Duplicate numbers should be output only once.
            

Example

            Input:
            5
            5
            5
            3
            2
            1

            Output:
            1
            2
            3
            5
            

Problem Solving Process

To solve this problem, follow these steps:

1. Input Acquisition: Accept the number of integers N and the N integers entered by the user.
2. Duplicate Removal: Remove any duplicate integers from the input.
3. Sorting: Sort the remaining integers in ascending order.
4. Output: Implement a function to output the sorted numbers.

I will provide code examples for each step in Kotlin below.

Code Implementation

            
            fun main() {
                // Read the number of integers N from the first line.
                val n = readLine()!!.toInt()
                // Read N integers from the second line.
                val numbers = mutableSetOf() // Use Set to avoid duplicates

                // Read N integers and remove duplicates
                for (i in 1..n) {
                    numbers.add(readLine()!!.toInt())
                }

                // Convert to List and sort
                val sortedNumbers = numbers.toList().sorted()

                // Output the sorted result
                for (num in sortedNumbers) {
                    println(num)
                }
            }
            
            

This code works as follows:

• It first takes the number of integers N from the user. Then, through N repetitions, it accepts the integers.
• Each integer is added to mutableSetOf, which naturally removes duplicates.
• This is converted to a List using the toList() method, and sorted using sorted().
• Finally, the sorted results are printed.

Time Complexity Analysis

Analyzing the time complexity of this problem:

• The process of reading the integers takes O(N), and using a Set for checking duplicates takes O(1) on average.
• Transforming all elements of the Set to a List and sorting takes O(M log M), where M is the number of unique numbers.
• Consequently, the time complexity is O(N + M log M).

Conclusion

In this lesson, we reviewed basic data structures and sorting algorithms in Kotlin through the problem of sorting numbers. Kotlin has strengths in utilizing Sets and Lists, and using these effectively can simplify many problems. The next lesson will cover more complex algorithm problems, so please look forward to it.

Problem Description

In this lecture, we will discuss a simple sorting algorithm problem called “Sorting Numbers 1.” The task is to sort the given numbers in ascending order. The requirements of the problem are as follows:

Problem: An integer N is given. Write a program that sorts these numbers in ascending order and outputs one number per line.

Input Format

• The first line contains the integer N (1 ≤ N ≤ 100,000)
• From the second line, N integers are given. (The range of the numbers is -1,000,000,000 ≤ integer ≤ 1,000,000,000)

Output Format

Output the sorted numbers in ascending order, one per line.

Example Input

    5
    5
    4
    3
    2
    1
    

Example Output

    1
    2
    3
    4
    5
    

Process of Solving the Problem

To solve this problem, we need to use a sorting algorithm. Kotlin provides built-in sorting methods, making it easy to solve the problem. Below is the process of solving the problem.

1. Receiving Input

First, we need to receive input. We will read the integer N and the array of integers through standard input. In Kotlin, we can use the readLine() method to get input.

2. Creating the Number Array

We need to convert the input numbers into an integer array and store them. To do this, we use the split() method along with the map() method.

3. Sorting

To sort the organized number array in ascending order, we can use Kotlin’s sort() method. This is very efficient and intuitive.

4. Outputting the Results

To output the sorted array one by one, we can iterate through the array and print the values.

Code Implementation

Now let’s implement all these processes into a single Kotlin program. Below is the code that solves the problem.

fun main() {
        // 1. Receiving Input
        val n = readLine()!!.toInt()
        val numbers = IntArray(n)

        // 2. Creating the Number Array
        for (i in 0 until n) {
            numbers[i] = readLine()!!.toInt()
        }

        // 3. Sorting
        numbers.sort()

        // 4. Outputting the Results
        for (number in numbers) {
            println(number)
        }
    }

Code Explanation

The above code executes each step in order. First, it uses readLine()!!.toInt() to read the integer N from the first line, and then saves N integers into an array using a loop. After that, it calls numbers.sort() to sort the array, and finally prints the sorted results.

Efficiency

The time complexity of this algorithm is O(N log N). This is a characteristic performance of sorting algorithms, and it works well even for large datasets. Given that N can go up to 100,000 within the specified range, it is a sufficiently efficient solution.

Conclusion

In this lecture, we covered the basics of algorithm problem-solving using Kotlin through a simple number sorting problem. It is important to build foundational problem-solving skills before tackling more complex problems. Gaining experience by solving various problems is the best way to improve.

Thank you, and I hope this helps you prepare for your coding tests!

Author: [Author Name]

Date: [Date]

Introduction

In coding tests, various problems are presented to evaluate algorithm problem-solving abilities. Among these, the “Sorting Numbers” problem is fundamental yet requires important algorithmic thinking. This problem aims to provide an opportunity to understand basic sorting algorithms and become familiar with the syntax of the Kotlin language.

Problem Description

Write a program to sort a given number of integers in ascending order.
The first line of input contains the integer N, followed by N lines each containing an integer.
Write a program that sorts these integers and outputs them one per line.

Input

        - The first line contains an integer N (1 ≤ N ≤ 1,000,000)
        - The next N lines each contain an integer A (1 ≤ A ≤ 1,000,000)
        

Output

        - Print the N integers sorted in ascending order, one per line
        

Problem Approach

This problem is a basic one that requires a sorting algorithm. Among various sorting algorithms,
utilizing the built-in features of Kotlin is useful.
We will solve the problem through the following steps.

1. Receiving input
2. Applying the sorting algorithm
3. Outputting the sorted result

1. Receiving Input

In Kotlin, you can use the readLine() function to take standard input.
Read the integer N from the first line and store the next N integers in an array or list.

Below is an example code used for receiving input.

            fun main() {
                val n = readLine()!!.toInt()
                val numbers = ArrayList()
                for (i in 1..n) {
                    numbers.add(readLine()!!.toInt())
                }
                // Following is sorting and output code
            }
        

2. Applying the Sorting Algorithm

In Kotlin, you can easily sort a list using the sorted() function.
This function sorts by default in ascending order, so it can be used without additional implementation.
You can apply sorting as follows.

            val sortedNumbers = numbers.sorted()
        

3. Outputting the Sorted Result

To print the sorted list, you can use a loop.
Simply output each element one per line.
To do this, you can use the forEach function.

            sortedNumbers.forEach { println(it) }
        

Complete Code

The complete code combining all the steps described above is as follows.

            fun main() {
                val n = readLine()!!.toInt()
                val numbers = ArrayList()
                
                for (i in 1..n) {
                    numbers.add(readLine()!!.toInt())
                }

                val sortedNumbers = numbers.sorted()

                sortedNumbers.forEach { println(it) }
            }
        

Complexity Analysis

The time complexity of the sorting algorithm used in this problem is generally O(N log N).
Therefore, it can efficiently handle sorting up to 1,000,000 integers.

Conclusion

The “Sorting Numbers” problem is greatly helpful in learning basic algorithms and the syntax of Kotlin.
To solve algorithm problems, it’s important to solidify the basics and practice with various problems.
I hope you continue to learn and practice different algorithms to prepare thoroughly for coding tests.

In this section, we will study various problems necessary to enhance coding skills and learn about the algorithm for finding prime numbers. A prime number is a natural number that can only be divided by 1 and itself. Prime numbers play an important role in mathematics and frequently appear in various algorithm problems. Learning efficient algorithms to solve these problems is a great help in preparing for coding interviews.

Problem Description

Write an algorithm to find all prime numbers that are less than or equal to the given natural number N.

Input

• Natural number N (2 ≤ N ≤ 100,000)

Output

• Print all prime numbers less than or equal to N in one line, separated by spaces.

Approach to the Problem

There are several methods to find prime numbers, but here we will use the Sieve of Eratosthenes algorithm. This algorithm is one of the most efficient ways to find all prime numbers within a given range. In particular, it is very efficient with a time complexity of O(n log log n), making it suitable for finding large prime numbers.

What is the Sieve of Eratosthenes?

The Sieve of Eratosthenes proceeds through the following steps:

1. List all natural numbers from 2 to N.
2. Since 2 is prime, remove all of its multiples (4, 6, 8, …).
3. Next, consider the smallest remaining number (3) as prime, and remove all of its multiples (6, 9, …).
4. Repeat this process up to the square root of N, and all remaining numbers are prime.

Code Implementation

Kotlin Code

fun sieveOfEratosthenes(n: Int): List {
    val isPrime = BooleanArray(n + 1) { true }
    isPrime[0] = false // 0 is not prime
    isPrime[1] = false // 1 is not prime

    for (i in 2..Math.sqrt(n.toDouble()).toInt()) {
        if (isPrime[i]) {
            for (j in i * i..n step i) {
                isPrime[j] = false // multiples of i are not prime
            }
        }
    }

    return (2..n).filter { isPrime[it] } // return list of primes
}

fun main() {
    val n = readLine()!!.toInt()
    val primes = sieveOfEratosthenes(n)
    println(primes.joinToString(" ")) // print primes
}
    

Code Explanation

The above code implements the Sieve of Eratosthenes algorithm using Kotlin. Now, let’s take a look at each part:

• BooleanArray(n + 1) { true }: Initializes all numbers up to N as prime.
• isPrime[0] = false and isPrime[1] = false: Set 0 and 1 as false because they are not prime.
• Math.sqrt(n.toDouble()).toInt(): Iterates up to the square root of N to check for primes.
• for (j in i * i..n step i): Loop to set multiples of prime i to false.
• (2..n).filter { isPrime[it] }: Finally returns the list of primes.

Algorithm Analysis

The time complexity of this algorithm is O(n log log n). This is very efficient for the problem of finding prime numbers. The space complexity is O(n). Using this algorithm, prime numbers up to 100,000 can be found very quickly.

Test Cases

Now let’s look at some test cases to verify that the algorithm works correctly.

Test Case 1

• Input: 10
• Output: 2 3 5 7

Test Case 2

• Input: 30
• Output: 2 3 5 7 11 13 17 19 23 29

Test Case 3

• Input: 1
• Output: (no output)

Conclusion

In this tutorial, we used the Sieve of Eratosthenes algorithm to find prime numbers. This algorithm is a common problem in coding tests, so it is essential to master it. Understanding each step of the algorithm carefully and testing it against various input values to validate its effectiveness is important.

In the future, we will cover various coding test problems using Kotlin. Continue learning, and focus on understanding the efficiency and functioning principles of each algorithm. Happy coding!

Problem Definition

Problem: Find the minimum palindromic prime number among all prime numbers within a given range.
A prime number is a natural number that has no divisors other than 1 and itself, while a palindromic number is a number that reads the same forwards and backwards.
The input consists of two integers A and B, representing the range from A to B inclusive.

Input Example

    Input: 10 100
    

Output Example

    Output: 101
    

Problem Solving Process

To solve this problem, I will approach it in the following steps.

Step 1: Implement Prime Check Function

First, I will implement a function to check for prime numbers. A prime number is a number that is only divisible by 1 and itself.
To determine if a number is prime, it’s sufficient to check for divisibility by all integers from 2 to √n.

    fun isPrime(num: Int): Boolean {
        if (num < 2) return false
        for (i in 2..Math.sqrt(num.toDouble()).toInt()) {
            if (num % i == 0) return false
        }
        return true
    }
    

Step 2: Implement Palindrome Check Function

Once the primality check is implemented, I will implement the palindrome check. This can be done by converting the number to a string
and checking if it is the same as its reverse.

    fun isPalindrome(num: Int): Boolean {
        val str = num.toString()
        return str == str.reversed()
    }
    

Step 3: Find Prime & Palindromic Numbers

I will check all integers in the given range from A to B, verifying if each number is both prime and a palindrome.

    fun findMinPalindromicPrime(A: Int, B: Int): Int? {
        var minValue: Int? = null
        for (num in A..B) {
            if (isPrime(num) && isPalindrome(num)) {
                if (minValue == null || num < minValue) {
                    minValue = num
                }
            }
        }
        return minValue
    }
    

Step 4: Integrate into Main Function

Finally, I will write the main function to call all of the above functions and output the result.
This will include taking user input and implementing the functionality to find the minimum value within the range.

    fun main() {
        val (A, B) = readLine()!!.split(" ").map { it.toInt() }
        val result = findMinPalindromicPrime(A, B)
        
        if (result != null) {
            println("Minimum palindromic prime: $result")
        } else {
            println("There are no palindromic primes in the given range.")
        }
    }
    

Summary

Now, let's summarize what we have implemented. The complete code is as follows.

    fun isPrime(num: Int): Boolean {
        if (num < 2) return false
        for (i in 2..Math.sqrt(num.toDouble()).toInt()) {
            if (num % i == 0) return false
        }
        return true
    }

    fun isPalindrome(num: Int): Boolean {
        val str = num.toString()
        return str == str.reversed()
    }

    fun findMinPalindromicPrime(A: Int, B: Int): Int? {
        var minValue: Int? = null
        for (num in A..B) {
            if (isPrime(num) && isPalindrome(num)) {
                if (minValue == null || num < minValue) {
                    minValue = num
                }
            }
        }
        return minValue
    }

    fun main() {
        val (A, B) = readLine()!!.split(" ").map { it.toInt() }
        val result = findMinPalindromicPrime(A, B)
        
        if (result != null) {
            println("Minimum palindromic prime: $result")
        } else {
            println("There are no palindromic primes in the given range.")
        }
    }
    

Conclusion

This article explained in detail how to determine primes and palindromes using Kotlin, and how to find the minimum value.
Such problem-solving techniques are often included in algorithm questions for job interviews, so practicing them would be beneficial.
Always try to solve various problems to continuously improve your skills.