You are given a list of lists of strings regions, where each list regions[i] defines a containment relationship such that the first region regions[i][0] directly contains all the subsequent regions regions[i][j] for $j \geq 1$.

If region $A$ contains region $B$ and region $B$ contains region $C$, then region $A$ also indirectly contains region $C$.

Given two specific regions region1 and region2, return the smallest region that contains both region1 and region2.

Constraints:

• $2 \leq$ regions.length $\leq 10^4$

• $2 \leq$ regions[i].length $\leq 20$

• $1 \leq$ regions[i][j].length, region1.length, region2.length $\leq 20$

• region1 $\neq$ region2

• regions[i][j], region1, and region2 consist of English letters.

• The input is generated such that there exists a region which contains all the other regions, either directly or indirectly.

• A region cannot be directly contained in more than one region.

Now, let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Implement your solution in the following coding playground.