题目描述：

Given a word, you need to judge whether the usage of capitals in it is right or not.

We define the usage of capitals in a word to be right when one of the following cases holds:

  1. All letters in this word are capitals, like “USA”.
  2. All letters in this word are not capitals, like “leetcode”.
  3. Only the first letter in this word is capital if it has more than one letter, like “Google”.

Otherwise, we define that this word doesn’t use capitals in a right way.

Example 1:

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Input: "USA"
Output: True

Example 2:

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Input: "FlaG"
Output: False

Note: The input will be a non-empty word consisting of uppercase and lowercase latin letters.

遍历一遍字符串，记录大写字母的出现次数与首字母是否大写，然后根据题目要求返回结果就可以了。

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class Solution {
public:
    bool detectCapitalUse(string word) {
        if (word.empty()) return true;
        int capitalNum = 0;
        int firstCapital = isupper(word[0]);
        
        for (auto c : word) {
            if (isupper(c)) capitalNum++;
        }
        
        return (capitalNum == 0 || capitalNum == word.length() || (firstCapital && capitalNum == 1));
    }
};