## A. Find Array

### Solution:

Obviously, when x>0, x cannot be divisible by x+1. Therefore, we can set a[i]=a[i-1]+1.

### Code:

Java

C++

## B. Build the Permutation

### Solution:

First, the difference between a and b cannot exceed 1. From the figure below, we can see that to link two "a" (blue), there must be a "b" (red):

The structure is shown in the figure below:

### Code:

Java

C++

## C. Game Master

### Solution:

First of all, if someone has the greatest strength in a certain picture, then he must be able to win.

And if one person may win, then if another person can defeat this person on a certain picture, then the other person also may win.

So we can use recursion directly.

### Code:

Java

C++

## D. Dominoes

The key to this problem is to find that WB and BW can be placed anywhere in most cases.