520. Detect Capital

Description

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:

All letters in this word are capitals, like "USA".
All letters in this word are not capitals, like "leetcode".
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.

Solution

分三种情况讨论：

• 首字母大写，合法的word是：
  • 从第二个字母开始，全大写；
  • 从第二个字母开始，全小写；
• 首字母小写，合法的word是：
  • 从第二个字母开始，全小写；

class Solution {
    public boolean detectCapitalUse(String word) {
        if (word.length() == 1) {
            return true;
        }
        
        return word.substring(1).equals(word.substring(1).toLowerCase())
                || (Character.isUpperCase(word.charAt(0)) 
                    && word.substring(1).equals(word.substring(1).toUpperCase()));
    }
}