Question

1684. Count the Number of Consistent Strings

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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, $C \leq 26$.

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 $O(1)$.

class Solution:
  def countConsistentStrings(self, allowed: str, words: List[str]) -> int:
    def f(w):
      return reduce(or_, (1 << (ord(c) - ord('a')) for c in w))

    mask = f(allowed)
    return sum((mask | f(w)) == mask for w in words)

class Solution {
  public int countConsistentStrings(String allowed, String[] words) {
    int mask = f(allowed);
    int ans = 0;
    for (String w : words) {
      if ((mask | f(w)) == mask) {
        ++ans;
      }
    }
    return ans;
  }

  private int f(String w) {
    int mask = 0;
    for (int i = 0; i < w.length(); ++i) {
      mask |= 1 << (w.charAt(i) - 'a');
    }
    return mask;
  }
}

class Solution {
public:
  int countConsistentStrings(string allowed, vector<string>& words) {
    auto f = [](string& w) {
      int mask = 0;
      for (auto& c : w) mask |= 1 << (c - 'a');
      return mask;
    };
    int mask = f(allowed);
    int ans = 0;
    for (auto& w : words) ans += (mask | f(w)) == mask;
    return ans;
  }
};

func countConsistentStrings(allowed string, words []string) (ans int) {
  f := func(w string) (mask int) {
    for _, c := range w {
      mask |= 1 << (c - 'a')
    }
    return
  }

  mask := f(allowed)
  for _, w := range words {
    if (mask | f(w)) == mask {
      ans++
    }
  }
  return
}

function countConsistentStrings(allowed: string, words: string[]): number {
  const helper = (s: string) => {
    let res = 0;
    for (const c of s) {
      res |= 1 << (c.charCodeAt(0) - 'a'.charCodeAt(0));
    }
    return res;
  };
  const mask = helper(allowed);
  let ans = 0;
  for (const word of words) {
    if ((mask | helper(word)) === mask) {
      ans++;
    }
  }
  return ans;
}

impl Solution {
  fn helper(s: &String) -> i32 {
    let mut res = 0;
    for c in s.as_bytes().iter() {
      res |= 1 << ((c - b'a') as i32);
    }
    res
  }

  pub fn count_consistent_strings(allowed: String, words: Vec<String>) -> i32 {
    let mask = Self::helper(&allowed);
    let mut ans = 0;
    for word in words.iter() {
      if (mask | Self::helper(word)) == mask {
        ans += 1;
      }
    }
    ans
  }
}

int helper(char* s) {
  int res = 0;
  int n = strlen(s);
  for (int i = 0; i < n; i++) {
    res |= 1 << (s[i] - 'a');
  }
  return res;
}

int countConsistentStrings(char* allowed, char** words, int wordsSize) {
  int mask = helper(allowed);
  int ans = 0;
  for (int i = 0; i < wordsSize; i++) {
    if ((mask | helper(words[i])) == mask) {
      ans++;
    }
  }
  return ans;
}