[leetcode]: 520. Detect Capital

1.题目
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”.
翻译：给定一个单词，判断它是否符合一下规则：
a. 全是大写，如”USA
b. 全是小写，如”leetcode”
c.只有首字母大写，如”Google”

2.分析
大致有两种解法：
（1）遍历一遍字符串，判断是否符合以上规则
（2）使用正则表达式匹配
或者，python还有函数可以直接调用，(solution里看到的)

3.代码
c++遍历

class Solution {
public:
    bool isCapital(char c) {
        return c >= 'A'&&c <= 'Z' ? true : false;
    }
    bool detectCapitalUse(string word) {
        if (word.size() <= 1)
            return true;
        else {
            bool first;
            if(!isCapital(word[0]))//首字母是小写，其他字母只能是小写
                first = isCapital(word[0]);
            else//首字母是大写，从第二个字母开始保持大小写一致
                first = isCapital(word[1]);
            bool result=false;
            for (int i = 1; i < word.size(); i++) {
                result = first^isCapital(word[i]);//异或，相同则为0，不同则为1
                if (result)
                    break;
            }
            return !result;
        }           
    }
};

c++正则表达式

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

python 直接调用函数

def detectCapitalUse(self, word):
    return word.isupper() or word.islower() or word.istitle()