Language: C++

//aの各要素を{選ぶ, 選ばない}で, 数列bを作ってみる。 -> aは相異なるのでbは相異なる。
//-> bの順番(r!通り)によらず, xor(b)は同じ値. (つまり, 各長さrについて, この作り方でhoge[r]通り作れたとすれば…
//答えはΣhoge[r] * r!になる。(選ぶ, 選ばない～でbを作る場合に必要な情報は [どこまで決めたか?, bの長さ, そこまでのxor]の3つ。これでDPすればよい）

#include <iostream>
#define int long long
using namespace std;

int mod = 1000000007;
int n, k;
int a[100];
int fact[101];
int dp[101][101][256];	//dp[id][len][xor] = count

signed main() {
	int id, len, xor;
	
	cin >> n >> k;
	for (id = 0; id < n; id++) cin >> a[id];
	fact[0] = 1; for (len = 1; len <= n; len++) { fact[len] = (fact[len - 1] * len) % mod; }
	
	dp[0][0][0] = 1;
	for (id = 0; id < n; id++) {
		for (len = 0; len <= id; len++) {
			for (xor = 0; xor < 256; xor++) {
				//使う
				dp[id + 1][len + 1][xor ^ a[id]] += dp[id][len][xor];
				//使わない
				dp[id + 1][len][xor] += dp[id][len][xor];
			}
		}
	}
	
	int ans = 0;
	for (len = 1; len <= n; len++) {
		ans += dp[n][len][k] * fact[len];
		ans %= mod;
	}
	cout << ans << endl;
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:16:22: error: expected unqualified-id before 'xor' token
   16 |         int id, len, xor;
      |                      ^~~
a.cc:25:30: error: expected primary-expression before 'xor' token
   25 |                         for (xor = 0; xor < 256; xor++) {
      |                              ^~~
a.cc:25:34: error: expected primary-expression before '=' token
   25 |                         for (xor = 0; xor < 256; xor++) {
      |                                  ^
a.cc:25:39: error: expected primary-expression before 'xor' token
   25 |                         for (xor = 0; xor < 256; xor++) {
      |                                       ^~~
a.cc:25:43: error: expected primary-expression before '<' token
   25 |                         for (xor = 0; xor < 256; xor++) {
      |                                           ^
a.cc:25:50: error: expected primary-expression before 'xor' token
   25 |                         for (xor = 0; xor < 256; xor++) {
      |                                                  ^~~
a.cc:25:55: error: expected primary-expression before ')' token
   25 |                         for (xor = 0; xor < 256; xor++) {
      |                                                       ^
a.cc:27:53: error: expected primary-expression before 'xor' token
   27 |                                 dp[id + 1][len + 1][xor ^ a[id]] += dp[id][len][xor];
      |                                                     ^~~
a.cc:27:57: error: expected primary-expression before '^' token
   27 |                                 dp[id + 1][len + 1][xor ^ a[id]] += dp[id][len][xor];
      |                                                         ^
a.cc:27:81: error: expected primary-expression before 'xor' token
   27 |                                 dp[id + 1][len + 1][xor ^ a[id]] += dp[id][len][xor];
      |                                                                                 ^~~
a.cc:27:84: error: expected primary-expression before ']' token
   27 |                                 dp[id + 1][len + 1][xor ^ a[id]] += dp[id][len][xor];
      |                                                                                    ^
a.cc:29:49: error: expected primary-expression before 'xor' token
   29 |                                 dp[id + 1][len][xor] += dp[id][len][xor];
      |                                                 ^~~
a.cc:29:52: error: expected primary-expression before ']' token
   29 |                                 dp[id + 1][len][xor] += dp[id][len][xor];
      |                                                    ^
a.cc:29:69: error: expected primary-expression before 'xor' token
   29 |                                 dp[id + 1][len][xor] += dp[id][len][xor];
      |                                                                     ^~~
a.cc:29:72: error: expected primary-expression before ']' token
   29 |                                 dp[id + 1][len][xor] += dp[id][len][xor];
      |                                                                        ^