c# - 在 List 中查找具有指定差异的数字

Question

对于给定的以空格分隔的数字列表，计算相差 N 的数字对总数的最有效方法是什么。

例如输入的命令行将是:

5 2

其中 5 是跟在后面的数字的个数，2 是所需的差值

1 5 3 4 2

要考虑的 5 个数字

输出应该是3个因为 (5,3)、(4,2) 和 (3,1) 的差都是 2

我可以让这个算法工作，但是如果你有大量的数字要处理，有没有更有效的方法呢？我已经包含了三个比较选项，第二个应该比第三个好，但是我忘记了什么可以让它更快吗？

private static void Difference()
{
    string[] firstInput = SplitInput(Console.ReadLine());

    int numberOfNumbers = int.Parse(firstInput[0]);
    int diffOfNumbers = int.Parse(firstInput[1]);

    string[] secondInput = SplitInput(Console.ReadLine());

    List<int> numbers = secondInput.Select(x => Int32.Parse(x)).ToList();

    int possibleCombinations = 0;

    // Option 1
    foreach (int firstNumber in numbers)
    {
        List<int> compareTo = numbers.GetRange(numbers.IndexOf(firstNumber) + 1, numbers.Count - numbers.IndexOf(firstNumber) - 1);

        foreach (int secondNumber in compareTo)
        {
            int diff = firstNumber - secondNumber;

            if (Math.Abs(diff) == diffOfNumbers)
            {
                possibleCombinations++;
            }
        }
    }

    // Option 2
    foreach (int firstNumber in numbers)
    {
        if (numbers.Contains(firstNumber + diffOfNumbers))
        {
                possibleCombinations++;
        }
    }

    // Option 3
    foreach (int firstNumber in numbers)
    {
        foreach (int secondNumber in numbers)
        {
            int diff = firstNumber - secondNumber;

            if(Math.Abs(diff) == diffOfNumbers)
            {
                possibleOptions++;
            }
        }
    }

    Console.WriteLine(string.Format("Possible number of options are: {0}", possibleCombinations));
    Console.ReadLine();
}

private static string[] SplitInput(string input)
{
    return input.Split(new char[1] { ' ' }, StringSplitOptions.RemoveEmptyEntries);
}

Answer 1

如果不允许或忽略重复数字(只计算唯一对)，您可以使用 HashSet<int> :

HashSet<int> myHashSet = ...
int difference = ...
int count;
foreach (int number in myHashSet)
{
    int counterpart = number - difference;
    if (myHashSet.Contains(counterpart))
    {
        count++;
    }
}