Count the Number of Consistent Strings

(#1684), Easy

Category: Array, Hash Table, String, Bit Manipulation, Counting

Problem Statement

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

Examples

Input: allowed = "ab", words = ["a", "b", "ab", "abc"]

Output: 3

Explanation:

Allowed characters are: 'a', 'b'
Word 1: 'a' → all characters allowed → ✅
Word 2: 'b' → all characters allowed → ✅
Word 3: 'ab' → all characters allowed → ✅
Word 4: 'abc' → contains 'c' which is not allowed → ❌
Total consistent strings = 3

Approach

Using Hash Set for Allowed Characters

Convert the `allowed` string into a Set to enable O(1) lookups for each character.
Initialize a counter variable `count` to keep track of consistent strings.
Loop through each word in the `words` array:
- For each word, check if every character exists in the Set using `.every()`.
- If the word is fully consistent, increment the `count`.
Return the final value of `count`.

var countConsistentStrings = function(allowed, words) {
  const allowedSet = new Set(allowed);
  let count = 0;

  for (const word of words) {
    let isConsistent = [...word].every(char => allowedSet.has(char));
    if (isConsistent) {
      count++;
    }
  }

  return count;
};

Complexity

Time: O(n * m), where n is the number of words and m is the average length of a word.

Space: O(k), where k is the number of unique characters in 'allowed'.

Watch Explanation

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