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int n, k;
cin >> n >> k;
vector<int> a(n);
for (auto &x : a) cin >> x;
 
int res = (k == 0);
int sum = 0;
 
for (int mask  = 1;  mask < (1 << n); mask++) {
    int diff = mask^(mask-1);
    while (diff != 0) {
        int idx = __builtin_ctz(diff); // idx = index on which mask and mask-1 differ(they could differ on many indices)
        diff ^= (1 << idx);
        if ((mask >> idx) & 1) { // mask has this bit set, but mask-1 hadn't
            sum += a[idx];
        } else { // mask hasn't this bit set, but mask-1 had
            sum -= a[idx];
        }
    }
    res += (sum == k);
}
 
cout << res;

prog.cpp:2:1: error: ‘cin’ does not name a type
 cin >> n >> k;
 ^~~
prog.cpp:3:1: error: ‘vector’ does not name a type
 vector<int> a(n);
 ^~~~~~
prog.cpp:4:1: error: expected unqualified-id before ‘for’
 for (auto &x : a) cin >> x;
 ^~~
prog.cpp:9:1: error: expected unqualified-id before ‘for’
 for (int mask  = 1;  mask < (1 << n); mask++) {
 ^~~
prog.cpp:9:22: error: ‘mask’ does not name a type
 for (int mask  = 1;  mask < (1 << n); mask++) {
                      ^~~~
prog.cpp:9:39: error: ‘mask’ does not name a type
 for (int mask  = 1;  mask < (1 << n); mask++) {
                                       ^~~~
prog.cpp:23:1: error: ‘cout’ does not name a type
 cout << res;
 ^~~~

Standard output is empty