c# - 在 C# 数组中避免重复操作的最有效方法是什么？

Question

我需要计算数组中每对点之间的距离，并且每对只想计算一次。我想出的方法是否足够有效或有更好的方法？这是一个示例，以及解释我要获取的内容的视觉效果:

例如，首先获取片段A-B、A-C、A-D；然后是 B-C，B-D；最后，C-D。换句话说，我们希望在新数组中使用 A-B，而不是 B-A，因为它会重复。

var pointsArray = new Point[4];

pointsArray[0] = new Point(0, 0);
pointsArray[1] = new Point(10, 0);
pointsArray[2] = new Point(10, 10);
pointsArray[3] = new Point(0, 10);

// using (n * (n-1)) / 2 to determine array size
int distArraySize = (pointsArray.Length*(pointsArray.Length - 1))/2;

var distanceArray = new double[distArraySize];

int distanceArrayIndex = 0;

// Loop through points and get distances, never using same point pair twice
for (int currentPointIndex = 0; currentPointIndex < pointsArray.Length - 1; currentPointIndex++)
{
    for (int otherPointIndex = currentPointIndex + 1;
            otherPointIndex < pointsArray.Length;
            otherPointIndex++)
    {
        double xDistance = pointsArray[otherPointIndex].X - pointsArray[currentPointIndex].X;
        double yDistance = pointsArray[otherPointIndex].Y - pointsArray[currentPointIndex].Y;

        double distance = Math.Sqrt(Math.Pow(xDistance, 2) + Math.Pow(yDistance, 2));

        // Add distance to distanceArray
        distanceArray[distanceArrayIndex] = distance;

        distanceArrayIndex++;
    }
} 

由于这将与数千个点一起使用，我认为精确尺寸的数组会比使用任何类型的 IEnumerable 更有效。

Answer 1

如果您有 n 个点，则所有点对的集合包含 n * (n-1)/2 个元素。那就是您正在执行的操作数。我要做的唯一改变是使用 Parallel.ForEach() 并行执行操作。

像这样(需要调试)

        int distArraySize = (pointsArray.Length * (pointsArray.Length - 1)) / 2;

        var distanceArray = new double[distArraySize];

        int numPoints = pointsArray.Length;

        Parallel.ForEach<int>(Enumerable.Range(0, numPoints - 2),
            currentPointIndex =>
            {
                Parallel.ForEach<int>(Enumerable.Range(currentPointIndex + 1, numPoints - 2),
                    otherPointIndex =>
                    {
                        double xDistance = pointsArray[otherPointIndex].X - pointsArray[currentPointIndex].X;
                        double yDistance = pointsArray[otherPointIndex].Y - pointsArray[currentPointIndex].Y;
                        double distance = Math.Sqrt(xDistance * xDistance + yDistance * yDistance);
                        int distanceArrayIndex = currentPointIndex * numPoints - (currentPointIndex * (currentPointIndex + 1) / 2) + otherPointIndex - 1;
                        distanceArray[distanceArrayIndex] = distance;
                    });
            });