在数组或列表中查找数字对

Question

My goal is to find pairs of numbers in an array or List. A pair in this case is defined by the maximum difference between two entries. For instance

1
50
2
100
102
800

Pairs(if max difference threshold is 2) with line numbers(array number):

1,2 line number of 1 is 0
100,101 line number of 100 is 3

How do I do this?

Answer 1

相反，这里没有库，您可以对数组进行排序，然后在循环中自动查找对。

Answer 2

I don't know of any library that would help you with this. You can use the methods in the framework.

For the case where threshold is 1, if you put the numbers from the array in a hash set you can efficiently look up the numbers that is a part of a pair:

HashSet<int> set = new HashSet<int>(myArray);
int[] pairs = myArray.Where(i => set.Contains(i + 1)).ToArray();

The pairs array will have the lower number of the pairs, eg { 1, 100 } when the pairs are 1, 2 and 100, 101 .

To get the index instead of the number, iterate the indexes instead:

HashSet<int> set = new HashSet<int>(myArray);
int[] index = Enumerable.Range(myArray.Length).Where(i => set.Contains(myArray[i + 1])).ToArray();

The index array will have the index of the lower numbers of the pairs.

Answer 3

You can use LINQ to do this:

var numbers = new[]
{
    1,
    50,
    2,
    100,
    102,
    800
};

var treshold = 2;

var numWithIndexes = numbers.Select((value, index) => new { value, index });

var pairs = from num1 in numWithIndexes
            from num2 in numWithIndexes
            where (num2.value - num1.value <= treshold) && (num2.value - num1.value > 0)
            select new[]
        {
            num1.value, // first number in the pair
            num2.value, // second number in the pair
            num1.index, // index of the first number in the pair
            num2.index  // index of the second member in the pair
        };

foreach (var pair in pairs)
{
    Console.WriteLine("Pair found: " + pair[0] + ", " + pair[1] +
                      " at line " + pair[2] + ", " + pair[3]);
}

Answer 4

Easily solved by sorting and then using a simple loop:

FindPairs(sequence: new[] { 1, 50, 2, 100, 101, 800 }, threshold: 2); // {1, 2}, {100, 101}.

private List<int[]> FindPairs(IEnumerable<int> sequence, int threshold)
{
    var sorted = sequence.OrderBy(x => x).ToList();

    var pairs = new List<int[]>();
    for (var i = 0; i < sorted.Count - 1; ++i)
    {
        if (sorted[i + 1] - sorted[i] <= threshold)
        {
            pairs.Add(new [] { sorted[i], sorted[i + 1] });
        }
    }

    return pairs;
}