520. detect capital

Given a non-empty string check if it can be constructed by taking a substring of it and appending multiple copies of the substring together. You may assume the given string consists of lowercase English letters only and its length will not exceed 10000.

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:

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Input: "USA"
Output: True

Example 2:

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Input: "FlaG"
Output: False

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class  {
    public boolean detectCapitalUse(String word) {
        if (word == null || word.length() < 2) {
            return true;
        }
        if (word.equals(word.toUpperCase())) {
            return true;
        }
        if (word.equals(word.toLowerCase())) {
            return true;
        }
        if (word.equals(word.charAt(0) + word.substring(1).toLowerCase())) {
            return true;
        }
        return false;
    }
}