1684. Count the Number of Consistent Strings

Description

You are given a string allowed consisting of distinct characters and an array of strings words. A string is consistent if all characters in the string appear in the string allowed.

Return the number of consistent strings in the array words.

Example 1:

Input: allowed = "ab", words = ["ad","bd","aaab","baa","badab"]
Output: 2
Explanation: Strings "aaab" and "baa" are consistent since they only contain characters 'a' and 'b'.

Example 2:

Input: allowed = "abc", words = ["a","b","c","ab","ac","bc","abc"]
Output: 7
Explanation: All strings are consistent.

Example 3:

Input: allowed = "cad", words = ["cc","acd","b","ba","bac","bad","ac","d"]
Output: 4
Explanation: Strings "cc", "acd", "ac", and "d" are consistent.

Constraints:

1 <= words.length <= 10⁴
1 <= allowed.length <=26
1 <= words[i].length <= 10
The characters in allowed are distinct.
words[i] and allowed contain only lowercase English letters.

Solutions

Solution 1: Hash Table or Array

A straightforward approach is to use a hash table or array $s$ to record the characters in allowed. Then iterate over the words array, for each string $w$, determine whether it is composed of characters in allowed. If so, increment the answer.

The time complexity is $O(m)$, and the space complexity is $O(C)$. Here, $m$ is the total length of all strings, and $C$ is the size of the character set allowed. In this problem, $C \leq 26$.

Python3JavaC++GoTypeScriptRustC

class Solution:
    def countConsistentStrings(self, allowed: str, words: List[str]) -> int:
        s = set(allowed)
        return sum(all(c in s for c in w) for w in words)

class Solution {
    public int countConsistentStrings(String allowed, String[] words) {
        boolean[] s = new boolean[26];
        for (char c : allowed.toCharArray()) {
            s[c - 'a'] = true;
        }
        int ans = 0;
        for (String w : words) {
            if (check(w, s)) {
                ++ans;
            }
        }
        return ans;
    }

    private boolean check(String w, boolean[] s) {
        for (int i = 0; i < w.length(); ++i) {
            if (!s[w.charAt(i) - 'a']) {
                return false;
            }
        }
        return true;
    }
}

class Solution {
public:
    int countConsistentStrings(string allowed, vector<string>& words) {
        bitset<26> s;
        for (auto& c : allowed) s[c - 'a'] = 1;
        int ans = 0;
        auto check = [&](string& w) {
            for (auto& c : w)
                if (!s[c - 'a']) return false;
            return true;
        };
        for (auto& w : words) ans += check(w);
        return ans;
    }
};

func countConsistentStrings(allowed string, words []string) (ans int) {
    s := [26]bool{}
    for _, c := range allowed {
        s[c-'a'] = true
    }
    check := func(w string) bool {
        for _, c := range w {
            if !s[c-'a'] {
                return false
            }
        }
        return true
    }
    for _, w := range words {
        if check(w) {
            ans++
        }
    }
    return ans
}

function countConsistentStrings(allowed: string, words: string[]): number {
    const set = new Set([...allowed]);
    const n = words.length;
    let ans = n;
    for (const word of words) {
        for (const c of word) {
            if (!set.has(c)) {
                ans--;
                break;
            }
        }
    }
    return ans;
}

impl Solution {
    pub fn count_consistent_strings(allowed: String, words: Vec<String>) -> i32 {
        let n = words.len();
        let mut make = [false; 26];
        for c in allowed.as_bytes() {
            make[(c - b'a') as usize] = true;
        }
        let mut ans = n as i32;
        for word in words.iter() {
            for c in word.as_bytes().iter() {
                if !make[(c - b'a') as usize] {
                    ans -= 1;
                    break;
                }
            }
        }
        ans
    }
}

int countConsistentStrings(char* allowed, char** words, int wordsSize) {
    int n = strlen(allowed);
    int make[26] = {0};
    for (int i = 0; i < n; i++) {
        make[allowed[i] - 'a'] = 1;
    }
    int ans = wordsSize;
    for (int i = 0; i < wordsSize; i++) {
        char* word = words[i];
        for (int j = 0; j < strlen(word); j++) {
            if (!make[word[j] - 'a']) {
                ans--;
                break;
            }
        }
    }
    return ans;
}

Solution 2: Bit Manipulation

We can also use a single integer to represent the occurrence of characters in each string. In this integer, each bit in the binary representation indicates whether a character appears.

We simply define a function $f(w)$ that can convert a string $w$ into an integer. Each bit in the binary representation of the integer indicates whether a character appears. For example, the string ab can be converted into the integer $3$, which is represented in binary as $11$. The string abd can be converted into the integer $11$, which is represented in binary as $1011$.

Back to the problem, to determine whether a string $w$ is composed of characters in allowed, we can check whether the result of the bitwise OR operation between $f(allowed)$ and $f(w)$ is equal to $f(allowed)$. If so, increment the answer.

The time complexity is $O(m)$, where $m$ is the total length of all strings. The space complexity is $O(1)$.