construct-note.js

// Frequency Counter - constructNote
// Write a function called constructNote, which accepts two strings, a message and some letters.
// The function should return true if the message can be built with the letters
// that you are given, or it should return false.
// Assume that there are only lowercase letters and no space or
// special characters in both the message and the letters.

// Bonus Constraints:
// If M is the length of message and N is the length of letters:
// Time Complexity: O(M+N)
// Space Complexity: O(N)

function constructNote(message, letters) {
  const obj = {};

  for (const char of letters) {
    obj[char] = ++obj[char] || 1;
  }

  for (const char of message) {
    if (!obj[char]) return false;
    obj[char]--;
  }

  return true;
}

console.log(constructNote('aa', 'abc')); // false
console.log(constructNote('abc', 'dcba')); // true
console.log(constructNote('aabbcc', 'bcabcaddff')); // true
console.log(constructNote('aabbcc', 'bc')); // false