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, 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.

题意：判断一个字符串大小写使用是否合法。合法的情况有：全为大写；全为小写；只有第一个字母大写。

算法1

题解：如果字符串长度为1，总是合法的；否则我们先判断一下前两个字符是否合法，当第一个字符为小写，第二个字符为大写时不合法；否则，后序所有字符大小写应该与第二个字符相同。

C++ 代码

class Solution {
public:
    int isupper(char c){ return ('A' <= c && c <= 'Z')?1:0;}
    int islower(char c){ return ('a' <= c && c <= 'z')?1:0;}
    bool detectCapitalUse(string word) {
        int n = word.length();
        if(n == 1) return true;
        if(islower(word[0]) && isupper(word[1])) return false;
        int upper = isupper(word[1]);
        for(int i = 2 ; i < n ; i ++)
            if(isupper(word[i]) ^ upper)
                return false;
        return true;     
    }
};