I’ve been trying this problem, and I received WA in 6/10 cases and AC in the other 4. My solution is pretty much plain brute force. I recursively replaced each `'_'`

with a `'1'`

and a `'0'`

and checked whether the number formed from each case was divisible by m, and incremented the answer accordingly. I can’t seem to figure out where I went wrong. Is my approach plain incorrect (though it’s unlikely), or have I made some stupid implementation mistake ?

Since the solutions aren’t public, I am pasting my code in a spoiler below.

## Spoiler

```
void rec(string s, int idx) {
if(idx == -1) {
ll nf = 0;
for(int i = n-1; i >= 0; i--) {
if(s[i] == '1') {
nf |= (1<<(n-1-i));
}
}
if(nf%m == 0) ans++;
} else {
if(s[idx] == '_') {
string scopy = s;
scopy[idx] = '1';
rec(scopy, idx - 1);
scopy[idx] = '0';
rec(scopy, idx - 1);
} else {
rec(s, idx - 1);
}
}
}
void solve() {
cin >> n >> m;
string s; cin >> s;
ans = 0;
rec(s, n-1);
cout << ans << "\n";
}
```