Hello and welcome to today's programming practice session! Are you prepared to delve into an exciting task involving nested loops and lists? Our focus today will be on mastering the use of nested loops to search two integer lists. You're about to embark on a fascinating journey of hands-on learning. Let's get started!

Imagine you've received two lists of integers. Should you choose to accept this mission, you'll need to write a method that locates and returns pairs of integers. The first element of the pair will come from the first list, with the second coming from the second list. It's important to note that the first element must be less than the second.

The order of pairs in your result should follow the order in which they appear in the input lists. For instance, given the lists List<int> list1 = {1, 3, 7}; and List<int> list2 = {2, 8, 9};, the method should return List<(int, int)> { (1, 2), (1, 8), (1, 9), (3, 8), (3, 9), (7, 8), (7, 9) }. It's a challenge if no pairs exist or if any input list is empty. Let's dissect this task to unravel the solution together!

Before we dive into writing code, let's break down the problem. It appears to be an ideal candidate for nested looping.

Begin by initializing a generic list called result, which will store our pairs.

C#
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1List<(int, int)> FindPairs(List<int> list1, List<int> list2)
2{
3    List<(int, int)> result = new List<(int, int)>();
4}

It's always prudent to set up your method and data storage first!

In this step, our focus shifts to the creation of nested loops. We'll need to iterate over both lists using foreach loops. One outer loop will pick an element from the first list, and an inner loop will skim through each element of the second list.

C#
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1List<(int, int)> FindPairs(List<int> list1, List<int> list2)
2{
3    List<(int, int)> result = new List<(int, int)>();
4    foreach (int i in list1)
5    {
6        foreach (int j in list2)
7        {
8            // We'll fill this in next
9        }
10    }
11    return result;
12}

In this context, i represents each element in list1, and for each i, j represents each element in list2.

Now that we have our loops established, let's introduce the logic inside. Here's where we make a crucial check: Is the element i from list1 less than the element j from list2? If it is, we append the pair (i, j) to our result list.

C#
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1List<(int, int)> FindPairs(List<int> list1, List<int> list2)
2{
3    List<(int, int)> result = new List<(int, int)>();
4    foreach (int i in list1)
5    {
6        foreach (int j in list2)
7        {
8            if (i < j)
9            {
10                result.Add((i, j));
11            }
12        }
13    }
14    return result;
15}

During each iteration of our inner loop, we make this check and store the pairs that meet our condition.

To help you understand how to run and see the output, let's add a Main method to demonstrate the implementation of the FindPairs method with example lists. This will make it easy to see the results of our nested loops in action.

C#
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1using System;
2using System.Collections.Generic;
3
4class Program
5{
6    static void Main(string[] args)
7    {
8        List<int> list1 = new List<int> { 1, 3, 7 };
9        List<int> list2 = new List<int> { 2, 8, 9 };
10        
11        List<(int, int)> pairs = FindPairs(list1, list2);
12        
13        Console.WriteLine("Pairs where the first element is less than the second:");
14        foreach (var pair in pairs)
15        {
16            Console.WriteLine($"({pair.Item1}, {pair.Item2})");
17        }
18    }
19
20    static List<(int, int)> FindPairs(List<int> list1, List<int> list2)
21    {
22        List<(int, int)> result = new List<(int, int)>();
23        foreach (int i in list1)
24        {
25            foreach (int j in list2)
26            {
27                if (i < j)
28                {
29                    result.Add((i, j));
30                }
31            }
32        }
33        return result;
34    }
35}

The Main method initializes two lists and calls the FindPairs method, displaying the pairs to confirm the implementation. After setting up and running the code, the output will show pairs where the first element is smaller than the second in the provided lists:

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1Pairs where the first element is less than the second:
2(1, 2)
3(1, 8)
4(1, 9)
5(3, 8)
6(3, 9)
7(7, 8)
8(7, 9)

This output confirms that the solution correctly identifies and lists all the valid pairs according to the problem's requirements.

Excellent job! You've successfully implemented a complex task using nested loops to search two lists. You now know how to traverse and manipulate two lists effectively to achieve your desired objective. Keep practicing and continually challenge yourself with more tasks to consolidate your knowledge. In your subsequent practice sessions, you will encounter similar challenges that will further enhance your understanding of this concept. Remember, practice is the key to mastering any concept. Happy coding!