kotlin coding test course, finding the greatest common divisor

Hello! In this session, we will delve into an algorithm problem that calculates the Greatest Common Divisor (GCD) using Kotlin. The GCD refers to the largest divisor that two or more integers share. This problem is one of those often encountered in programming interviews. Let’s take a look at the problem.

Problem Description

Given two integers A and B, write a function to calculate the GCD of these two numbers. For example, if A and B are 48 and 18 respectively, the GCD is 6.

Input Format

  • The first line contains the integer A. (1 ≤ A ≤ 109)
  • The second line contains the integer B. (1 ≤ B ≤ 109)

Output Format

Print the GCD of the two integers.

Problem Approach

There are several ways to find the GCD, but among them, the Euclidean algorithm is the most famous and efficient method. The Euclidean algorithm is based on the following principle:

  • GCD(A, B) = GCD(B, A % B) (until B becomes 0)
  • GCD(A, 0) = A

In other words, given two numbers A and B, we find the remainder of A divided by B, and during this process, when B becomes 0, we can identify that A is the GCD. This algorithm can find the GCD very quickly, proportional to the size of the two numbers.

Kotlin Implementation

Now, let’s implement the above algorithm in Kotlin. The code example is as follows:

fun gcd(a: Int, b: Int): Int {
    return if (b == 0) a else gcd(b, a % b)
}

fun main() {
    val a = readLine()!!.toInt()
    val b = readLine()!!.toInt()
    println(gcd(a, b))
}

The code above takes two integers as input and computes the GCD using the function, then prints the result.

Detailed Code Explanation

1. Function Definition

First, we define a function named gcd. This function takes two integers a and b as parameters.

2. Termination Condition

Inside the function, we check whether b is 0. If b is 0, the GCD is a, so we return a.

3. Recursive Call

If not, we recursively call gcd(b, a % b). This process continues until b becomes 0, calculating the GCD.

4. Main Function

In the main function, we use readLine() to take input of two integers from the user. This input is guaranteed to be non-null using !! and is converted to an integer type using toInt(). Finally, we call println(gcd(a, b)) to print the result.

Test Cases

Now, let’s verify whether this algorithm works correctly through test cases. Below are some sample test cases:

Test Case Number A B Expected Output Actual Output
1 48 18 6
2 56 98 14
3 101 10 1
4 7 13 1

Code Optimization

The implementation above is simple and easy to understand. However, it can also be implemented in a more optimized way. By using Kotlin’s built-in functions and APIs, we can achieve more concise code and better performance. For example, in Kotlin, you can also use the gcd function from the Math class. This can make the code more succinct:

fun main() {
    val a = readLine()!!.toInt()
    val b = readLine()!!.toInt()
    println(Math.gcd(a, b)) // This method is used in Java 8 and above
}

Conclusion

In this lecture, we explored a problem on calculating the GCD using Kotlin. We learned that it can be solved with a simple yet efficient method using the Euclidean algorithm.

It is important to encounter various problems while preparing for coding tests and to develop algorithmic thinking through the process of solving these problems. To succeed in your next coding test, you should implement actual code and test it in different scenarios.

If you have any further questions or requests for topics, please leave a comment! Thank you for reading!