LeetCode 3120: Count the Number of Special Characters I Solution

Master LeetCode problem 3120 (Count the Number of Special Characters I), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

3120. Count the Number of Special Characters I

Easy

Hash Table String

Problem Explanation

Explanation

To solve this problem, we can iterate through the characters in the input string and keep track of the lowercase and uppercase versions of each letter using a set. If we encounter a letter that is already in both lowercase and uppercase forms in the set, we increment a counter. Finally, we return the counter as the number of special characters in the input string.

Time Complexity: O(n) where n is the length of the input string.
Space Complexity: O(1) since the set will contain at most 26 characters (lowercase and uppercase English letters).

Solution Code

public int countSpecialCharacters(String word) {
    Set<Character> specialChars = new HashSet<>();
    int count = 0;
    
    for (char c : word.toCharArray()) {
        char lc = Character.toLowerCase(c);
        char uc = Character.toUpperCase(c);
        
        if (specialChars.contains(lc) && specialChars.contains(uc)) {
            count++;
        } else {
            specialChars.add(lc);
            specialChars.add(uc);
        }
    }
    
    return count;
}

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