Kotlin coding test course, determining the direction of a line segment

Coding tests are a commonly used method to evaluate the abilities of software developers. In particular, algorithm problem-solving skills are considered one of the important factors by many companies. In this course, we will explain the problem-solving process through a problem of determining the direction of a line segment, and we will write the code using the Kotlin language.

Problem Description

Given two points (x1, y1) and (x2, y2), write a program to determine the direction of the line segment formed by these two points. The direction is defined as follows:

  • If the line segment rotates clockwise, print ‘CW’.
  • If the line segment rotates counterclockwise, print ‘CCW’.
  • If the line segment is on a straight line, print ‘C’.

Input

  • First line: integers x1, y1 (coordinates of the first point)
  • Second line: integers x2, y2 (coordinates of the second point)

Output

Output the direction of the line segment in the format described above.

Problem-Solving Steps

1. Understanding the Problem

To understand the problem, let’s examine the geometric meaning of defining the direction of the line segment. A line segment represents a straight line between two points, and it is essential to determine whether this line makes a clockwise or counterclockwise angle. It will be useful to consider a third point based on the two points to decide the direction.

2. Utilizing the Cross Product of Vectors

To determine the direction of the line segment, we can use the cross product. By using the cross product, we can easily determine the direction of the angle formed by two vectors. The cross product of two vectors A and B is defined as follows:

A = (x2 – x1, y2 – y1), B = (x, y)

Here, B is the point chosen as a reference. Depending on the angle formed by A and the direction of B, we can judge whether it is clockwise, counterclockwise, or on a straight line.

3. Writing Kotlin Code


fun determineDirection(x1: Int, y1: Int, x2: Int, y2: Int): String {
    val direction = (x2 - x1) * (y2) - (y2 - y1) * (x2)

    return when {
        direction > 0 -> "CCW"
        direction < 0 -> "CW"
        else -> "C"
    }
}

4. Implementing and Testing the Complete Function

Let’s implement the complete program to receive input and outputting it in this format.


fun main() {
    val (x1, y1) = readLine()!!.split(" ").map { it.toInt() }
    val (x2, y2) = readLine()!!.split(" ").map { it.toInt() }

    println(determineDirection(x1, y1, x2, y2))
}

5. Explaining the Code

This code performs the function of accepting the coordinates of two points and outputting the direction of the line segment. The ‘determineDirection’ function uses the cross product to calculate the direction, returning ‘CCW’, ‘CW’, or ‘C’ based on the result. The ‘main’ function takes two points’ coordinates from the user and passes them to the function to output the result.

Conclusion

In this course, we examined the process of solving the problem of determining the direction of a line segment. Using the cross product of vectors to determine direction is a very useful approach when solving geometric problems. In the future, when encountering advanced algorithmic problems or geometry-related issues, this foundational knowledge can be applied to solve more complex problems. I hope this process of solving the problem using Kotlin has helped deepen your understanding of the programming language’s syntax and the properties of data structures.

References

  • Algorithm Problem-Solving Strategies – Author: Koo Jong-man
  • Kotlin Programming – Author: Jason Edmond

If you found this post interesting and useful, please check out other courses as well!