CF1174D Ehab and the Expected XOR Problem

Given two integers $ n $ and $ x $ , construct an array that satisfies the following conditions: - for any element $ a_i $ in the array, $ 1 \le a_i

The only line contains two integers $ n $ and $ x $ ( $ 1 \le n \le 18 $ , $ 1 \le x

The first line should contain the length of the array $ l $ . If $ l $ is positive, the second line should contain $ l $ space-separated integers $ a_1 $ , $ a_2 $ , $ \dots $ , $ a_l $ ( $ 1 \le a_i < 2^n $ ) — the elements of the array $ a $ . If there are multiple solutions, print any of them.

In the first example, the bitwise XOR of the subsegments are $ \{6,7,4,1,2,3\} $ .