C#实现列表/数组元素相加所有可能组合技术求助

Hey there! Let's figure out how to adjust your code to work with an int[] array instead of a List<int>, plus fix a small issue in your original List-based code to make it more robust.

First, let's spot the small problem in your original code #

Your current code uses a hardcoded 4 for the loop limits, which works only if your initial List has exactly 4 elements. If you ever change the initial array, this will break. A better approach is to capture the initial count of the List first, then loop against that:

int initialListCount = List.Count;
for (int noSelected = 0; noSelected < initialListCount; noSelected++)
{
    for(int noAdded = 0; noAdded < initialListCount; noAdded++)
    {
        List.Add(List[noSelected] + List[noAdded]);
    }
}

This way, it'll work no matter how many elements you start with.

Now, let's implement this for an int[] array #

The core idea is the same: iterate over all pairs of elements, calculate their sum, collect those sums, then remove duplicates. Using a HashSet<int> is more efficient here because it automatically handles duplicates as we add elements, instead of collecting everything first and then calling Distinct().

Here's the full code:

namespace CombinationWork
{
    class Program
    {
        static void Main(string[] args)
        {
            // Your input int array
            int[] a = new int[] { 1, 2, 5, 10 };
            
            // HashSet automatically handles duplicate sums
            HashSet<int> uniqueSums = new HashSet<int>();
            
            // Iterate over all pairs (including element + itself)
            for (int i = 0; i < a.Length; i++)
            {
                for (int j = 0; j < a.Length; j++)
                {
                    uniqueSums.Add(a[i] + a[j]);
                }
            }
            
            // Output each unique sum
            foreach (int sum in uniqueSums)
            {
                Console.WriteLine(sum);
            }
            
            Console.ReadLine();
        }
    }
}

Why use HashSet instead of List? #

• Efficiency: HashSet checks for duplicates when adding each element, so you avoid the extra step of filtering duplicates later with Distinct().
• Cleaner code: It's more intuitive to use a collection that's designed for unique values when that's exactly what you need.

If you prefer to stick with a List (maybe for specific ordering needs), you can do this instead:

List<int> allSums = new List<int>();
for (int i = 0; i < a.Length; i++)
{
    for (int j = 0; j < a.Length; j++)
    {
        allSums.Add(a[i] + a[j]);
    }
}
// Remove duplicates and convert back to List
List<int> uniqueSums = allSums.Distinct().ToList();

Just note this is slightly less efficient since it first collects all sums (including duplicates) before filtering.

内容的提问来源于stack exchange，提问作者Khwaja Hussam Quasmi