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:

• 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.

Code:

class Solution {
    public boolean detectCapitalUse(String word) {
        String lowerCaseWord = word.toLowerCase();
        int difference = 0;
        for (int i = 0; i < word.length(); i++) {
            if (word.charAt(i) != lowerCaseWord.charAt(i)) difference += 1;
        }
        
        if (difference == 0 || difference == word.length()) return true;
        if (difference == 1 && word.charAt(0) != lowerCaseWord.charAt(0)) return true;
        return false;
    }
}

解题思路：

• 首先将字符串全部转换成小写，使用word.toLowerCase();
• 比较原字符串和新字符串的不一样的个数；
• 如果difference为0或word.length()，则返回真；
• 如果有且只有开头一个字符不等，也返回真；
• 其余情况返回假。