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

思路一：

检查输入的单词是否符合大小写规则。符合规则的情况有：全部大写，全部小写，首字母大写。设置计数器count统计大写字母的个数，则三种符合规则的情况可以表示为：count=单词长度，count=0，及count=1且首字母大写。

Code：

class Solution {public:    bool detectCapitalUse(string word) {        int count=0;        for(int i=0; i<word.size();i++){            if(word[i]>='A'&&word[i]<='Z') count++;        }        if(count==0||count==word.size()) return true;        else if(count==1&&word[0]<='Z') return true;        else return false;    }};

思路二：

使用正则表达式。注：regex_match()是正则表达式匹配的函数。+：1 or more；*：0 or more。 

Code：

class Solution {public:    bool detectCapitalUse(string word) {        return regex_match(word, regex("[A-Z]+|[a-z]+|[A-Z][a-z]*"));    }};