从范围中选择但排除某些数字 [英] Select from a range but exclude certain numbers

问题描述

Is it possible to pick a random number from a given range (1-90), but exclude certain numbers. The excluded numbers are dynamically created but lets say they are 3, 8, and 80.

I have managed to create random number generator but couldn't identify any functions that let me fulfill my requirements.

Random r = new Random();
this.num = r.Next(1, 90);

The numbers which are to be excluded are previously generated numbers. So, if the random number is one, this would then get added to the excluded numbers list.

解决方案

Using some handy extension methods here, you can create a range of numbers and select randomly from that rage. For example, with these extension methods:

public static T RandomElement(this IEnumerable<T> enumerable)
{
    return enumerable.RandomElementUsing(new Random());
}

public static T RandomElementUsing(this IEnumerable<T> enumerable, Random rand)
{
    int index = rand.Next(0, enumerable.Count());
    return enumerable.ElementAt(index);
}

You can apply these to a filtered range of numbers:

var random = Enumerable.Range(1, 90).Except(arrayOfRemovedNumbers).RandomElement();

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