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0520 - Detect Capital (Easy)

https://leetcode.com/problems/detect-capital/

Problem Statement​

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.

Approach 1: One Pass​

Just check if it is invalid the conditions. If so, return false immediately.

Written by @wingkwong
class Solution {
public:
    bool detectCapitalUse(string word) {
        for(int i = 1; i < word.size(); i++){
            if(isupper(word[1]) != isupper(word[i]) || 
               islower(word[0]) && isupper(word[i])) return false;
        }        
        return true;
    }
};

Approach 2: Case By Case​

Count the number of characters with upper case and try those 3 cases.

Written by @wingkwong
class Solution {
public:
    bool detectCapitalUse(string word) {
        int upper = 0;
		// count number of characters with upper case
        for (auto x : word) upper += isupper(x) ? 1 : 0;
            // case 1: All letters in this word are capitals, like "USA".
        return upper == word.size() ||
            // case 2: All letters in this word are not capitals, like "leetcode".
               upper == 0 ||
            // case 3: Only the first letter in this word is capital, like "Google".
               (upper == 1 && isupper(word.front()));
    }
};