#953 - Verifying an Alien Dictionary

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Problem Description

In an alien language, surprisingly, they also use English lowercase letters, but possibly in a different order. The order of the alphabet is some permutation of lowercase letters.

Given a sequence of words written in the alien language, and the order of the alphabet, return true if and only if the given words are sorted lexicographically in this alien language.

Solution

/**
 * @param {string[]} words
 * @param {string} order
 * @return {boolean}
 */
var isAlienSorted = function(words, order) {
  const map = new Map(order.split('').map((char, index) => [char, index]));

  for (let i = 0; i < words.length - 1; i++) {
    if (!helper(words[i], words[i + 1])) return false;
  }

  return true;

  function helper(word1, word2) {
    for (let i = 0; i < word1.length; i++) {
      if (i >= word2.length) return false;
      const char1 = map.get(word1[i]);
      const char2 = map.get(word2[i]);
      if (char1 < char2) return true;
      if (char1 > char2) return false;
    }
    return true;
  }
};