DetectCapitalRunTime.cs

public bool DetectCapitalUse(string word)
{
    var capitals = 0;
    for (var i = 0; i < word.Length; i++)
    {
        if (char.IsUpper(word[i])) capitals++;
    }

    if (capitals == word.Length || capitals == 0) return true;
    return capitals == 1 && char.IsUpper(word[0]);
}