Pangram - FreeCodeCamp #24 Daily-Challenge

Pangram: Analysis and Explanation

Problem Statement

Given a word or phrase and a string of lowercase letters, determine if the phrase:

• Uses all the letters from the set at least once.
• Does not use any letter outside that set.

Uppercase, spaces, and punctuation should be ignored.

Initial Analysis

Understanding the Problem

The function receives:

1. A word or phrase (may include uppercase, spaces, and punctuation).
2. A string with the allowed letters (lowercase).

What must the phrase satisfy?

• Use all allowed letters at least once.
• Not use any extra letter.
• Ignore uppercase, spaces, and punctuation.

Key Test Cases

Solution Development

Strategy

We use Set to compare the unique letters in the phrase with the allowed ones:

1. Normalize the phrase: lowercase and only letters.
2. Create a Set with the unique letters from the phrase.
3. Create a Set with the allowed letters.
4. Compare both Sets:
   • If they have the same size and all letters from the phrase are in the allowed set, it’s a valid pangram.
   • Otherwise, it’s invalid.

Flowchart (Mermaid)

flowchart TD
  A["Start"] --> B["Receive phrase and letters"]
  B --> C["Normalize: lowercase and only letters"]
  C --> D["Set of phrase letters"]
  D --> E["Set of allowed letters"]
  E --> F{"Same size?"}
  F -- No --> G["false"]
  F -- Yes --> H{"All letters in allowed set?"}
  H -- No --> G
  H -- Yes --> I["true"]
  G --> J["End"]
  I --> J
  classDef decision fill:#fef3c7,stroke:#92400e,stroke-width:2px,color:#000;
  classDef process fill:#dbeafe,stroke:#1e3a8a,stroke-width:1px;
  classDef startend fill:#dcfce7,stroke:#166534,stroke-width:2px;
  class A,J startend;
  class B,C,D,E process;
  class F,H decision;

Final Code

/**
 * Determines if a phrase is an exact pangram for a given set of letters.
 * @param {string} sentence - Phrase to analyze
 * @param {string} letters - Allowed letters (lowercase)
 * @returns {boolean}
 */
function isPangram(sentence, letters) {
  // 1. Normalize: lowercase and only letters
  const normalized = sentence.toLowerCase().replace(/[^a-z]/g, '')
  // 2. Set of unique letters in the phrase
  const sentenceSet = new Set(normalized)
  // 3. Set of allowed letters
  const lettersSet = new Set(letters)
  // 4. Compare size and content
  if (sentenceSet.size !== lettersSet.size)
    return false
  return [...sentenceSet].every(l => lettersSet.has(l))
}
export default isPangram

Complexity Analysis

Time Complexity

• Time: $O(n + m)$, where $n$ is the length of the phrase and $m$ is the length of the allowed letters. We traverse the phrase to clean and extract letters, and the set of letters to compare.
• Space: $O(m)$, for the two Sets (allowed and present letters).

Edge Cases and Considerations

• Empty phrase: false
• Missing any letter: false
• Extra letter present: false
• Uppercase, spaces, and punctuation are ignored
• Empty allowed letters: false

Reflections and Learnings

What did we learn?

• Set is ideal for validating uniqueness and membership.
• Cleaning and normalizing strings is key in text problems.
• Comparing sets is a powerful technique for exact validations.

Can it be optimized?

• The Set approach is already optimal for this case.
• If you validate many phrases with the same set, precompute the allowed set once.

Resources and References

• MDN Set Documentation
• JavaScript Regular Expressions