#281 Foreign Dictionary

Given a list of words sorted lexicographically in a foreign language that uses lowercase latin letters in a different order, determine the ordering of the letters in that language.

Rules:

• Words are sorted lexicographically where:
  • First different letter determines order (smaller letter comes first)
  • If no different letters found, shorter word comes first
• Return empty string if order is invalid
• If multiple valid orders exist, return any of them

Constraints:

• 1 ≤ words.length ≤ 100
• 1 ≤ words[i].length ≤ 100
• Words contain only lowercase letters a-z

Examples:

// Example 1:
const words1 = ["z", "o"];
console.log(alienOrder(words1));
// Output: "zo"
// Explanation: 'z' comes before 'o' in this language

// Example 2:
const words2 = ["hrn", "hrf", "er", "enn", "rfnn"];
console.log(alienOrder(words2));
// Output: "hernf"
// Explanation:
// hrn vs hrf: n < f
// hrf vs er: h < e
// er vs enn: r < n
// enn vs rfnn: e < r
// One valid order is "hernf"