520. Detect Capital

题目：

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.

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

3/31/2017

13%, 51ms

用了自带的函数，如果用Python连第三种情况都可以直接title()来比较

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()

别人的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，我更喜欢这个

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

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

这个方法也很聪明：ascii码当中，大写在小写之前，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));
    }
}

朴实但是很聪明的解法，比较大写的数量和位置。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();
    }

更多讨论：

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