leetcode 520[easy]---Detect Capital

难度：easy

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.

思路：题目啰啰嗦嗦一大堆，简而言之就是只有符合 1. 全是大写 2.全是小写  3. 只有首字母是大写 三个条件之一的string才是True，否则就是false

          用 str.islower() 和str.isupper() 判读，一行code搞定