Marc Lester Tan

The easiest way to solve this problem is to count the number of uppercase character. We can easily do that by using map and Character.isUpperCase functions.

class Solution {
    fun detectCapitalUse(word: String): Boolean {
        return word.map { if(Character.isUpperCase(it)) 1 else 0 }.sum().let {
            return it == word.length || 
                it == 1 && Character.isUpperCase(word[0]) || 
                it == 0    
        }
        
    }
}

Runtime: 160 ms, faster than 52.00% of Kotlin online submissions for Detect Capital.
Memory Usage: 32.7 MB, less than 100.00% of Kotlin online submissions for Detect Capital.

According to the description, there are 3 criterias to determine if the word is using the capitalization correctly:

1. All are capital
2. First character is capital
3. Zero capital characters

These criterias can be easily represented by the sum of all uppercase characters:

sum == word.length || sum == 1 && Character.isUpperCase(word[0]) || sum == 0