在处理大量迭代时，是否有比在C＃的for循环中嵌套if语句更有效的替代方法？

Question

I have a method which consists of an if statement nested within a for loop:

for (int i = 0; i < val; i=i+2)
{
    for (int j = i+1; j < val; j=j+1)
    {
        actualDistance = actualDistance + (ulong)Math.Max(revenue[i], revenue[j]) * (ulong)Math.Abs(point[j] - point[i]);

        if (j + 1 < val)
        {
            actualDistance = actualDistance + (ulong)Math.Max(revenue[i+1], revenue[j+1]) * (ulong)Math.Abs(point[j+1] - point[i+1]);
        }
    }
}

However, if val represents a number within the tens of millions, then the method takes a very long time during runtime since it is used in both the for and if loops.

Is there a better and more efficient way of doing this? The code as it currently stands is too time inefficient.

Answer 1

Either I'm missing something or your code is equivalent to:

for (int j = i+1; j < val; j=j+1)
{
    actualDistance = actualDistance + (ulong)Math.Max(revenue[i], revenue[j]) * (ulong)Math.Abs(point[j] - point[i]);

    actualDistance = actualDistance + (ulong)Math.Max(revenue[i+1], revenue[j+1]) * (ulong)Math.Abs(point[j+1] - point[i+1]);
}

actualDistance = actualDistance - (ulong)Math.Max(revenue[i+1], revenue[val]) * (ulong)Math.Abs(point[val] - point[i+1])

Your if statement will be almost always true and the only case when it's false is when j == val - 1 , so you can just always run the code inside if statement and than subtract that last case outside of for loop.