Check if any item in a list matches any item in another list

Question

A coleague asked me to write a one-liner to replace the following method:

public static bool IsResourceAvailableToUser(IEnumerable<string> resourceRoles, IEnumerable<string> userRoles)
{
    foreach (var userRole in userRoles)
        foreach (var resourceRole in resourceRoles)
            if (resourceRole == userRole)
                return true;
    return false;
}

Resharper and I came up with this:

public static bool IsResourceAvailableToUser(IEnumerable<string> resourceRoles, IEnumerable<string> userRoles)
{
    return userRoles.Where(resourceRoles.Contains).Count() > 0;
}

Is there a better way?

Answer 1

Given LINQ, yes:

return userRoles.Intersect(resourceRoles).Any();

Note that aside from the use of Intersect to turn it into O(m) + O(n) instead O(m * n), using Any is more efficient than using Count() > 0 - you know the answer as soon as you've found the first match.