97. Alien Dictionary

PRO

Hard

Topics

Companies

Helpful tools to learn & understand

Visualize LogicActive Simulator

Watch key transitions, pointers, and variables update step-by-step.

Open

Check Solutions

Read clean, documented implementations across multiple patterns.

View Code

Thinkpad (Draw & Note)

Sketch diagrams on an infinite canvas and draft notes directly inline.

Draw

Example 1:

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

Output: "wertf"

Explanation: The correct order is "wertf" based on the given words.

Example 2:

Input: words = ["z","x"]

Output: "zx"

Explanation: The correct order is "zx" based on the given words.

Example 3:

Input: words = ["z","x","z"]

Output: ""

Explanation: The input contains contradictory information, so an empty string is returned.

Example 4:

Input: words = ["abc","ab"]

Output: ""

Explanation: The input contains contradictory information, so an empty string is returned.

Example 5:

Input: words = ["a","b","ca","cc"]

Output: "abc"

Explanation: Based on the input, a comes before b, b comes before c, so the order is abc.

Constraints:

•
•
•
•

Time Complexity

O(C) (≈ O(V + E))

Space Complexity

O(V + E)