kotlin coding test course, create the maximum value by grouping numbers

Problem Description

Input Format

First line: integer n (size of the array)
Second line: n integers (elements of the array)

Output Format

Output the maximum value.

Solution Process

This problem is an algorithmic challenge that applies a methodology for grouping numbers in order to maximize the product of two numbers. To solve this issue, we need to follow several steps.

1. Data Analysis

First, let’s analyze the properties of the numbers we have. In the case of positive numbers, multiplying the two largest numbers is advantageous for obtaining the maximum product. Conversely, for negative numbers, multiplying two negatives will yield a positive number, so utilizing the two smallest negative numbers is beneficial for finding the maximum product. Therefore, we need to consider the following two cases:

• The product of the two largest positive numbers
• The product of the two smallest negative numbers

2. Algorithm Design

Based on the above cases, we can design an algorithm. First, we will explore all elements of the array to separate the positive and negative numbers, and then find the maximum and minimum values for each.

1. Find the two largest numbers among the positives.
2. Find the two smallest numbers among the negatives.
3. Compare their products to determine the maximum value.

3. Kotlin Implementation

Now, let’s implement the algorithm in Kotlin.

fun maxProduct(numbers: IntArray): Long {
    val positives = mutableListOf()
    val negatives = mutableListOf()

    for (num in numbers) {
        if (num > 0) {
            positives.add(num)
        } else if (num < 0) {
            negatives.add(num)
        }
    }

    positives.sortDescending()
    negatives.sort()

    var maxProduct = Long.MIN_VALUE

    if (positives.size >= 2) {
        maxProduct = maxOf(maxProduct, positives[0].toLong() * positives[1])
    }

    if (negatives.size >= 2) {
        maxProduct = maxOf(maxProduct, negatives[0].toLong() * negatives[1])
    }

    return maxProduct
}

4. Test Cases

Now let’s create a few test cases to validate the function we wrote.

fun main() {
    // Test case 1: All numbers are positive
    println(maxProduct(intArrayOf(1, 2, 3, 4))) // Output: 12

    // Test case 2: All numbers are negative
    println(maxProduct(intArrayOf(-1, -2, -3, -4))) // Output: 6

    // Test case 3: Mixed numbers
    println(maxProduct(intArrayOf(-1, 2, -3, 4))) // Output: 6

    // Test case 4: Combined numbers
    println(maxProduct(intArrayOf(-10, -20, 5, 3, -2))) // Output: 200

    // Test case 5: Including 0
    println(maxProduct(intArrayOf(0, -5, -1, 2))) // Output: 5
}

Conclusion

In this session, we learned about the ‘Maximize Product by Grouping Numbers’ problem, the algorithm design process, and Kotlin programming techniques. This problem provides an opportunity to practice basic data processing methods by analyzing and separating the elements in an array. By implementing this in Kotlin, we hope to gain a better understanding of how theory applies in practice. We encourage you to continue improving your algorithm skills through various problems.