520. Detect Capital

Problem

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, like "Google".

Given a string word, return true if the usage of capitals in it is right.

  Example 1:

Input: word = "USA"
Output: true

Example 2:

Input: word = "FlaG"
Output: false

  Constraints:

• 1 <= word.length <= 100

• word consists of lowercase and uppercase English letters.

Solution (Java)

class Solution {
    public boolean detectCapitalUse(String word) {
        if (word == null || word.length() == 0) {
            return false;
        }
        int upper = 0;
        int lower = 0;
        int n = word.length();
        boolean firstUpper = Character.isUpperCase(word.charAt(0));
        for (int i = 0; i < n; i++) {
            if (Character.isUpperCase(word.charAt(i))) {
                upper++;
            } else if (Character.isLowerCase(word.charAt(i))) {
                lower++;
            }
        }
        if (firstUpper && upper > 1) {
            firstUpper = false;
        }
        return upper == n || lower == n || firstUpper;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).