LeetCode 520. Detect Capital

[quinnwencn]

Description

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.

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Analysis

There are three cases in which the usage of capitals is right:

1. Start with Capital characters, and others are Uppercase.
2. Start with Capital characters, but others are all lowercase.
3. All characters are lowercase.

Solution written in Cpp

class Solution {
public:
    bool detectCapitalUse(string word) {
        constexpr char MAX = 'Z';
        if (word[0] <= MAX) { // start with Uppercase
            if (word.length() == 1) {
                return true;
            }

            bool isLowercase = word[1] > MAX;
            for (auto i = 1; i < word.length(); ++i) {
                if (word[i] <= MAX && isLowercase) {
                    return false;
                } else if (word[i] > MAX && !isLowercase) {
                    return false;
                }
            }
        } else {
            for (auto i = 1; i < word.length(); ++i) {
                if (word[i] <= MAX) {
                    return false;
                }
            }
        }

        return true;
    }
};

Solution written in Rust

impl Solution {
    pub fn detect_capital_use(word: String) -> bool {
        if word == word.to_uppercase() || word == word.to_lowercase() {
            return true;
        }
        if word.chars().skip(1).all(|c| c.is_lowercase()) {
            return true;
        }
        false
    }
}