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Check if the sentence is Pangram

Problem Description​

A pangram is a sentence where every letter of the English alphabet appears at least once. Given a string sentence containing only lowercase English letters, return true if sentence is a pangram, or false otherwise.

Examples​

Example 1:

Input: sentence = "thequickbrownfoxjumpsoverthelazydog"
Output: true
Explanation: sentence contains at least one of every letter of the English alphabet.

Example 2:

Input: sentence = "leetcode"
Output: false

Constraints​

  • 1 <= sentence.length <= 1000
  • sentence consists of lowercase English letters.

Solution for Check if the sentence is Pangram​

Approach​

Brute Force​

  • Create a set of all 26 letters of the English alphabet.
  • Iterate through each character in the sentence.
  • Remove each character from the set if it exists in the set.
  • After processing the entire sentence, check if the set is empty. If it is empty, it means every letter was found at least once in the sentence.

Complexity

  • Time Complexity: O(n), where n is the length of the sentence. This is because we need to iterate through each character of the sentence once.
  • Space Complexity: O(1), since the size of the alphabet set is fixed (26 letters).

Corner Cases:

  • An empty string should immediately return false.
  • A string shorter than 26 characters cannot be a pangram.
  • Strings with all letters but mixed with additional characters should still return true.

Recursive function:

def is_pangram_brute_force(sentence):
    # Define the set of all alphabet letters
    alphabet_set = set("abcdefghijklmnopqrstuvwxyz")
    
    # Iterate through each character in the sentence
    for char in sentence:
        # Remove the character from the alphabet set
        alphabet_set.discard(char)
        # If the set is empty, we found all the letters
        if not alphabet_set:
            return True
    
    # Check if the alphabet set is empty
    return len(alphabet_set) == 0

# Test cases
print(is_pangram_brute_force("thequickbrownfoxjumpsoverthelazydog"))  # Output: True
print(is_pangram_brute_force("leetcode"))  # Output: False

Optimized Approach​

  • Use a set to keep track of unique characters in the sentence.
  • Iterate through each character in the sentence and add it to the set.
  • After processing the entire sentence, check if the set contains 26 unique characters.

Complexity:

  • Time Complexity: O(n), where n is the length of the sentence. This is because we need to iterate through each character of the sentence once.
  • Space Complexity: O(1), since the maximum size of the set is 26 (the number of unique letters in the English alphabet).

Corner Cases:

  • Similar to the brute force approach: an empty string, a string shorter than 26 characters, and strings with all letters plus additional characters should be handled correctly.

Optimized Solution:

def is_pangram_optimized(sentence):
    # Use a set to store unique characters
    seen_characters = set()
    
    # Iterate through each character in the sentence
    for char in sentence:
        # Add the character to the set
        seen_characters.add(char)
        # If the set size is 26, it means we have seen all letters
        if len(seen_characters) == 26:
            return True
    
    # Check if we have 26 unique characters
    return len(seen_characters) == 26

# Test cases
print(is_pangram_optimized("thequickbrownfoxjumpsoverthelazydog"))  # Output: True
print(is_pangram_optimized("leetcode"))  # Output: False

Implementation​

Live Editor
function Solution(string) {
  var checkIfPangram = function(sentence) {
    // Use a set to store unique characters
    const seenCharacters = new Set();

    // Iterate through each character in the sentence
    for (const char of sentence) {
    // Add the character to the set
        seenCharacters.add(char);
        // If the set size is 26, it means we have seen all letters
        if (seenCharacters.size === 26) {
            return true;
        }
    }

// Check if we have 26 unique characters
    return seenCharacters.size === 26;
  };

  const input = "thequickbrownfoxjumpsoverthelazydog";
  const output = checkIfPangram(input);
  return (
    <div>
      <p>
        <b>Input: </b>
        {JSON.stringify(input)}
      </p>
      <p>
        <b>Output:</b> {output.toString()}
      </p>
    </div>
  );
}
Result
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Code in Different Languages​

Written by @vansh-codes
 /**
  * @param {string} sentence
  * @return {boolean}
  */
 var checkIfPangram = function(sentence) {
     const seenCharacters = new Set();
     
     for (const char of sentence) {
         seenCharacters.add(char);
         if (seenCharacters.size === 26) {
             return true;
         }
     }
     
     return seenCharacters.size === 26;
 };

References​