题目描述

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

Note: The input will be a non-empty word consisting of uppercase and lowercase latin letters.

解法一

思路

不妨看看哪些情况是不满足要求的：

  • ABCd，即有超过一个大写字母时，出现小写。
  • abCd，即有小写字母时，大写字母不在第一个。

所以当遍历字母时，只需要记录三个布尔变量saw_lower、saw_one_upper和saw_two_upper：

  • 字母是大写时：如果已经有小写字母（saw_lower == True），则返回False；否则，如果已经有大写字母（saw_one_upper == True）则置saw_two_upper为True，如果没有大写字母（saw_one_upper == False），则置saw_one_upper为True。
  • 字母是小写时：如果已经有两个大写字母（saw_two_upper == True），则返回False；否则，置saw_lower为True。
  • 如果处理过程中途未返回，则返回True。

Python

class Solution(object):
    def detectCapitalUse(self, word):
        """
        :type word: str
        :rtype: bool
        """
        saw_lower = False
        saw_one_upper = False
        saw_two_upper = False
        for letter in word:
            if letter >= 'A' and letter <= 'Z':
                if saw_lower:
                    return False
                if saw_one_upper:
                    saw_two_upper = True
                else:
                    saw_one_upper = True
            if letter >= 'a' and letter <= 'z':
                if saw_two_upper:
                    return False
                saw_lower = True
        return True

Java

public class Solution {
    public boolean detectCapitalUse(String word) {
        boolean sawLower = false;
        boolean sawOneUpper = false;
        boolean sawTwoUpper = false;
        for (char letter : word.toCharArray()) {
            if (letter >= 'A' && letter <= 'Z') {
                if (sawLower) {
                    return false;
                }
                if (sawOneUpper) {
                    sawTwoUpper = true;
                } else {
                    sawOneUpper = true;
                }
            }
            if (letter >= 'a' && letter <= 'z') {
                if (sawTwoUpper) {
                    return false;
                }
                sawLower = true;
            }
        }
        return true;
    }
}

C++

class Solution {
public:
    bool detectCapitalUse(string word) {
        bool sawLower = false;
        bool sawOneUpper = false;
        bool sawTwoUpper = false;
        for (auto letter : word) {
            if (letter >= 'A' && letter <= 'Z') {
                if (sawLower) {
                    return false;
                }
                if (sawOneUpper) {
                    sawTwoUpper = true;
                } else {
                    sawOneUpper = true;
                }
            }
            if (letter >= 'a' && letter <= 'z') {
                if (sawTwoUpper) {
                    return false;
                }
                sawLower = true;
            }
        }
        return true;
    }
};