LeetCode 269 Alien Dictionary - Problem Statement

Given a list of words sorted lexicographically in an alien language, infer the character order.

With words = ["wrt","wrf","er","ett","rftt"]:

• "wrt" < "wrf" means 't' < 'f' (first difference at index 2).
• "wrf" < "er" means 'w' < 'e'.
• "er" < "ett" means 'r' < 't'.
• "ett" < "rftt" means 'e' < 'r'.

Character order: "wertf".

If no valid ordering exists (cycle or invalid input), return "".

Constraints: $1 \le$ words.length $\le 100$. $1 \le$ word length $\le 100$.