[LeetCode] 520. Detect Capital

520. Detect Capital

• Hardness: \(\color{green}\textsf{Easy}\)
• Ralated Topics: String

一、題目

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.

二、分析

• 這題只需要判斷簡單的 if-else 即可解題。
• 根據題意，要馬全是大寫，要馬全是小寫，不然就是只有首字大寫。

三、解題

1. String

• Time complexity: \(O(n)\)
• Space complexity: \(O(1)\)

bool detectCapitalUse(string word) {
    if (word.length() == 1) return true;
    if (word[0] >= 'a') {                   // 小寫
        for (int i = 1; i < word.length(); i++){
            char& c = word[i];
            if (c < 'a') return false;
        } 
    } else {                                // 大寫
        if (word[1] < 'a') {                // 大寫+大寫
            for (int i = 2; i < word.length(); i++) {
                char& c = word[i];
                if (c >= 'a') return false;
            }
        } else {                            // 大寫+小寫
            for (int i = 2; i < word.length(); i++) {
                char& c = word[i];
                if (c < 'a') return false;
            }
        }
    }
    return true;
}

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