LeetCode Entry

3120. Count the Number of Special Characters I

26.05.2026 easy 2026 kotlin rust

Count letters with both cases

3120. Count the Number of Special Characters I easy substack youtube

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Problem TLDR

Count letters with both cases

Intuition

Brute-force is accepted. O(n) memory: for any uniq lowercase check if uppercase present, use hashset O(1) memory: two bitmasks, for lower and for upper cases; (m & M) count bits is the result

Approach

• regex is ugly here

Complexity

• Time complexity: \(O(n^2)\)

• Space complexity: \(O(n)\)

Code

    fun numberOfSpecialChars(w: String) =
        w.toSet().count {it-32 in w}

    pub fn number_of_special_chars(w: String) -> i32 {
        ('a'..='z').zip('A'..='Z').filter(|&(c,C)| w.contains(c)&&w.contains(C)).count() as _
    }