520.md

520. Detect Capital

Description

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.

Thinking Process

1. Keep 3 flags firstLetterCapital, canBeCapital, canBeNonCapital
2. Scan through the list, whenever a lowercase letter appears canBeCapital = false, whenever more than 1 capitals appear, canBeNonCapital = false

Code

public class Solution {
    public boolean detectCapitalUse(String word) {
        boolean firstLetterCapital = false;
        boolean canBeCapital = true;
        boolean canBeNonCapital = true;
        for(int i = 0; i < word.length(); i++){
            char c = word.charAt(i);
            if(c >= 'A' && c <= 'Z'){
                if(i == 0)
                    firstLetterCapital = true;
                else if(!firstLetterCapital)
                    return false;
                else if(!canBeCapital)
                    return false;
                else if(canBeCapital)
                    canBeNonCapital = false;
            }else{
                canBeCapital = false;
                if(!canBeNonCapital)
                    return false;
            }
        }
        return true;
    }
}

Complexity

1. Time complexity is O(n) as the string is scanned once