Question

Suppose I have a list of strings, like this:

var candidates = new List<String> { "Peter", "Chris", "Maggie", "Virginia" };

Now I’d like to verify that another List<String>, let’s call it list1, contains each of those candidates exactly once.
How can I do that, succintly? I think I can use Intersect(). I also want to get the missing candidates.

private bool ContainsAllCandidatesOnce(List<String> list1)
{
     ????
}


private IEnumerable<String> MissingCandidates(List<String> list1)
{
     ????
}

Order doesn’t matter.

Answer 1

This may not be optimal in terms of speed, but both queries are short enough to fit on a single line, and are easy to understand:

private bool ContainsAllCandidatesOnce(List<String> list1)
{
    return candidates.All(c => list1.Count(v => v == c) == 1);
}

private IEnumerable<String> MissingCandidates(List<String> list1)
{
    return candidates.Where(c => list1.Count(v => v == c) != 1);
}