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Count the Number of Consistent Strings

Difficulty: Easy

Problem 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.

Key Insights

  • A string is considered consistent if all its characters belong to the set of characters defined in allowed.
  • The characters in allowed are distinct, which simplifies the checking process.
  • We can use a set data structure to efficiently check character membership.
  • The solution needs to iterate through each word in the words array and determine if it is consistent.

Space and Time Complexity

Time Complexity: O(n * m), where n is the number of words and m is the maximum length of a word, since we check each word character by character. Space Complexity: O(k), where k is the size of the allowed string, for storing the characters in a set.

Solution

To solve the problem, we can use a set to store the characters from the allowed string. Then, for each word in the words array, we check if all characters in that word are present in the set. If they are, we count that word as consistent. This approach leverages the efficiency of set lookups to ensure that our solution is optimal.

Code Solutions

def countConsistentStrings(allowed, words):
    allowed_set = set(allowed)  # Create a set of allowed characters
    count = 0  # Initialize a counter for consistent strings
    
    for word in words:
        # Check if all characters in the word are in the allowed_set
        if all(char in allowed_set for char in word):
            count += 1  # Increment count if the word is consistent
            
    return count  # Return the total count of consistent strings
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