LeetCode 520. Detect Capital

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:

Input: "USA"
Output: True

Example 2:

Input: "FlaG"
Output: False

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

这道题晕死我了，我以为是一定要等于USA或者leetcode才让过，然后剩下的单词就是第一个字母大写，结果怎么都提交不对，后来实在没辙想着去搜下别人的答案吧，结果，发现是我理解错了= =、、

var detectCapitalUse = function(word) {
    return /^([A-Z]+|[a-z]+|[A-Z][a-z]+)$/.test(word);  
    
};

正则表达式就搞定了！