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:
- 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".
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.
一開始沒多想，就只是單純使用 ascii 來判斷大小寫，前面判斷長度，則是為了避免 ArrayOutOfBound 錯誤
class Solution {
public boolean detectCapitalUse(String word) {
char[] wordElements = word.toCharArray();
int wordLength = word.length();
if(wordLength == 1) {
return true;
}
if(isLower(wordElements[0])) {
for(int i=1; i<wordLength; i++) {
if(isUpper(wordElements[i])) return false;
}
} else if (isUpper(wordElements[0]) && isUpper(wordElements[1])) {
for(int i=2; i<wordLength; i++) {
if(isLower(wordElements[i])) return false;
}
} else if (isUpper(wordElements[0]) && isLower(wordElements[1])) {
for(int i=2; i<wordLength; i++) {
if(isUpper(wordElements[i])) return false;
}
}
return true;
}
private boolean isUpper(char element) {
return element >= 65 && element <= 90;
}
private boolean isLower(char element) {
return element >= 97 && element <= 122;
}
}
後來研究了其他人解法發現可以直接使用 String 所提供的 toUpperCase 和 toLowerCase 直接比較是否全大寫或全小寫
而字首大寫其他部分小寫，則可以用 Character 的 isUpperCase 搭配即可
public boolean detectCapitalUse(String word) {
return word.equals(word.toUpperCase()) ||
word.equals(word.toLowerCase()) ||
Character.isUpperCase(word.charAt(0)) &&
word.substring(1).equals(word.substring(1).toLowerCase());
}
除此之外，最方便的應該還是使用正規表示式
? 代表出現 0 或 1 次
* 則是出現 0 或 1 次以上
public boolean detectCapitalUse(String word) {
return word.matches("[A-Z]*|[A-Z]?[a-z]*");
}
參考網址
https://www.javaworld.com.tw/jute/post/view?bid=20&id=130126
https://leetcode.com/problems/detect-capital/discuss/99298/Java-1-Liner
https://leetcode.com/problems/detect-capital/discuss/99274/Simple-Java-Solution-O(n)-time-O(1)-space