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: Bit Manipulation

• Time complexity: O(10n)
• Space complexity: O(1)

 

JavaScript

/**
 * @param {string} allowed
 * @param {string[]} words
 * @return {number}
 */
const countConsistentStrings = function (allowed, words) {
  const BASE_CODE = 'a'.charCodeAt(0);
  const MAX_ALLOWED = 26;
  let mask = 1 << MAX_ALLOWED;

  for (const letter of allowed) {
    const code = letter.charCodeAt(0) - BASE_CODE;

    mask ^= 1 << code;
  }

  return words.reduce((result, word) => {
    let current = mask;

    for (const letter of word) {
      const code = letter.charCodeAt(0) - BASE_CODE;

      current |= 1 << code;
    }
    return result + (current === mask ? 1 : 0);
  }, 0);
};