520. Detect Capital

題目：

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:

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.

鏈接：https://leetcode.com/problems/detect-capital/#/description

3/31/2017

13%, 51ms

用了自帶的函數，如果用Python連第三種情況都可以直接title()來比較

public class Solution {
    public boolean detectCapitalUse(String word) {
        if (word.equals(word.toUpperCase()) || word.equals(word.toLowerCase())) return true;
        if (word.charAt(0) >= 'A' && word.charAt(0) <= 'Z' && word.substring(1, word.length()).equals(word.substring(1, word.length()).toLowerCase())) return true;
        return false;
    }
}

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

別人的regex方法，但是需要53ms

public boolean detectCapitalUse(String word) {
    return word.matches("[A-Z]+|[a-z]+|[A-Z][a-z]+");
}

或者，我更喜歡這個

public boolean detectCapitalUse(String word) {
    return word.matches("[A-Z]*|[A-Z]?[a-z]*");
}

https://discuss.leetcode.com/topic/79930/java-1-liner/3

這個方法也很聰明：ascii碼當中，大寫在小寫之前，只需要29ms

https://discuss.leetcode.com/topic/79912/3-lines

public class Solution {
    public boolean detectCapitalUse(String word) {
        int cnt = 0;
        for(char c: word.toCharArray()) if('Z' - c >= 0) cnt++;
        return ((cnt==0 || cnt==word.length()) || (cnt==1 && 'Z' - word.charAt(0)>=0));
    }
}

樸實但是很聰明的解法，比較大寫的數量和位置。34ms，注意Character.isUpperCase

https://discuss.leetcode.com/topic/79911/simple-java-solution-o-n-time-o-1-space

    public boolean detectCapitalUse(String word) {
        int numUpper = 0;
        for (int i=0;i<word.length();i++) {
            if (Character.isUpperCase(word.charAt(i))) numUpper++;
        }
        if (numUpper == 1) return Character.isUpperCase(word.charAt(0));
        return numUpper == 0 || numUpper == word.length();
    }

更多討論：

https://discuss.leetcode.com/category/668/detect-capital