C# Coding Test Course, Finding Minimum Value 2

Problem Description

Write a function to find the two smallest numbers in the given integer array and return their sum.

Example:

            Input: [3, 1, 4, 1, 5, 9, 2, 6, 5]
            Output: 2 (1 + 1)
            

If the same number is included, the same number can be used twice.

Approach to the Problem

We can consider several approaches to solve this problem.

1. Using Sorting

We can sort the array and then take the first two elements to calculate their sum.

2. Using Nested Loops

It is also possible to find the minimum values by directly comparing two integers using nested loops. However, this method may be inefficient.

3. Finding Minimum Values Using a Single Loop

The method of finding the two smallest numbers using a single loop is the most efficient. It allows you to find the minimum values while iterating through the array only once.

Solution Method 1: Using Sorting

using System;
using System.Linq;

public class Solution {
    public static int FindTwoMinSum(int[] arr) {
        // Sort the array.
        Array.Sort(arr);
        // Return the sum of the two smallest numbers.
        return arr[0] + arr[1];
    }
}

// Example usage
public class Program {
    public static void Main() {
        int[] numbers = {3, 1, 4, 1, 5, 9, 2, 6, 5};
        Console.WriteLine(FindTwoMinSum(numbers)); // Output: 2
    }
}
            

This method is intuitive and easy to understand, but it has a time complexity of O(n log n), which can be relatively slow. Performance degradation is a concern, especially for large array sizes.

Solution Method 2: Using Nested Loops

using System;

public class Solution {
    public static int FindTwoMinSum(int[] arr) {
        int min1 = int.MaxValue;
        int min2 = int.MaxValue;

        foreach (int num in arr) {
            if (num < min1) {
                min2 = min1;
                min1 = num;
            } else if (num < min2) {
                min2 = num;
            }
        }
        
        return min1 + min2;
    }
}

// Example usage
public class Program {
    public static void Main() {
        int[] numbers = {3, 1, 4, 1, 5, 9, 2, 6, 5};
        Console.WriteLine(FindTwoMinSum(numbers)); // Output: 2
    }
}
            

This method has a time complexity of O(n), making it more efficient. It finds the two smallest numbers while iterating through the array only once. While this method excels in performance, it does introduce a bit of code complexity.

Conclusion

In this article, we explored various ways to solve the problem of finding the two smallest values in a given array using C#. The first method, using sorting, is simple to implement but lacks in performance. In contrast, the approach utilizing a single loop is efficient and practical. Such problems often appear in algorithm tests, so it is essential to practice and achieve a good understanding.

Learning various problem-solving methods will be beneficial not only for coding tests but also in actual development environments. Thank you.