LeetCode-520. Detect Capital

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

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

基本思路：

由题可知，字符的长度>=1。

当字符串长度等于1时，任何字符串都符合要求；

当字符串长度大于1时，符合要求的字符串有三种，全是大写字母、全是小写字母、首字符为大写其余字符为小写字母。

class Solution {
    public boolean detectCapitalUse(String word) {
        int firstLetter = -1;        
        if(word.length()<2)return true;
        if(Character.isLowerCase(word.charAt(0))&&!Character.isLowerCase(word.charAt(1)))
            return false;        
        if(!Character.isLowerCase(word.charAt(0))&&!Character.isLowerCase(word.charAt(1)))
            firstLetter = 0;
        if(Character.isLowerCase(word.charAt(0))&&Character.isLowerCase(word.charAt(1)))
            firstLetter = 1;
        if(!Character.isLowerCase(word.charAt(0))&&Character.isLowerCase(word.charAt(1)))
            firstLetter = 2;
        if(firstLetter == 0){
            for(int i=2;i<word.length();i++){
                if(Character.isLowerCase(word.charAt(i))==true)
                    return false;
            }
        } else{
            for(int i=2;i<word.length();i++){
                if(Character.isLowerCase(word.charAt(i))==false)
                    return false;
            }
        }
        return true;
    }
}

进阶思路：

符合要求的字符串有三种情况：全大写、全小写、第一个大写其余小写。

全大写意味着字符串中大写字符的个数=word.length();

全小写意味着字符串中大写字符的个数=0;

第一个大写意味着字符串中大写字符的个数=1且字符串的首字符是大写。

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

终极思路：

/*
全大写 [A-Z]+
全小写 [a-z]+
第一个大写其余小写 [A-Z][a-z]+
*/
class Solution {
    public boolean detectCapitalUse(String word) {
        return word.matches("[A-Z]+|[a-z]+|[A-Z][a-z]+");
    }
}