README_EN.md

comments	difficulty	edit_url	rating	source	tags
true	Easy	https://github.com/doocs/leetcode/edit/main/solution/3100-3199/3120.Count%20the%20Number%20of%20Special%20Characters%20I/README_EN.md	1205	Weekly Contest 394 Q1	Hash Table String

3120. Count the Number of Special Characters I

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Description

You are given a string word. A letter is called special if it appears both in lowercase and uppercase in word.

Return the number of special letters in word.

 

Example 1:

Input: word = "aaAbcBC"

Output: 3

Explanation:

The special characters in word are 'a', 'b', and 'c'.

Example 2:

Input: word = "abc"

Output: 0

Explanation:

No character in word appears in uppercase.

Example 3:

Input: word = "abBCab"

Output: 1

Explanation:

The only special character in word is 'b'.

 

Constraints:

• 1 <= word.length <= 50
• word consists of only lowercase and uppercase English letters.

Solutions

Solution 1: Hash Table or Array

We use a hash table or array $s$ to record the characters that appear in the string $word$. Then we traverse the 26 letters. If both the lowercase and uppercase letters appear in $s$, the count of special characters is incremented by one.

Finally, return the count of special characters.

The time complexity is $O(n + |\Sigma|)$, and the space complexity is $O(|\Sigma|)$. Where $n$ is the length of the string $word$, and $|\Sigma|$ is the size of the character set. In this problem, $|\Sigma| \leq 128$.

Python3

class Solution:
    def numberOfSpecialChars(self, word: str) -> int:
        s = set(word)
        return sum(a in s and b in s for a, b in zip(ascii_lowercase, ascii_uppercase))

Java

class Solution {
    public int numberOfSpecialChars(String word) {
        boolean[] s = new boolean['z' + 1];
        for (int i = 0; i < word.length(); ++i) {
            s[word.charAt(i)] = true;
        }
        int ans = 0;
        for (int i = 0; i < 26; ++i) {
            if (s['a' + i] && s['A' + i]) {
                ++ans;
            }
        }
        return ans;
    }
}

C++

class Solution {
public:
    int numberOfSpecialChars(string word) {
        vector<bool> s('z' + 1);
        for (char& c : word) {
            s[c] = true;
        }
        int ans = 0;
        for (int i = 0; i < 26; ++i) {
            ans += s['a' + i] && s['A' + i];
        }
        return ans;
    }
};

Go

func numberOfSpecialChars(word string) (ans int) {
	s := make([]bool, 'z'+1)
	for _, c := range word {
		s[c] = true
	}
	for i := 0; i < 26; i++ {
		if s['a'+i] && s['A'+i] {
			ans++
		}
	}
	return
}

TypeScript

function numberOfSpecialChars(word: string): number {
    const s: boolean[] = Array.from({ length: 'z'.charCodeAt(0) + 1 }, () => false);
    for (let i = 0; i < word.length; ++i) {
        s[word.charCodeAt(i)] = true;
    }
    let ans: number = 0;
    for (let i = 0; i < 26; ++i) {
        if (s['a'.charCodeAt(0) + i] && s['A'.charCodeAt(0) + i]) {
            ++ans;
        }
    }
    return ans;
}