ARC 084 F XorShift

http://arc084.contest.atcoder.jp/tasks/arc084_d

多項式への言い換えが気持ちがいい問題だった。多項式は気持ちがいい。

#include <iostream>
#include <algorithm>
#include <vector>
 
using namespace std;

const long long mod = 998244353;

string gcd(string a, string b) {
  while (true) {
    if (a.size() < b.size()) swap(a, b);
    for (int i = 0; i < b.size(); i++) {
      a[i] ^= b[i];
    }
    int pos = a.find(1);
    if (pos == string::npos) return b;
    a.erase(0, pos);
  }
}

string input() {
  string s;
  cin >> s;
  for (char &c : s) c -= '0';
  return s;
}

long long modpow(long long x, long long y) {
  long long ret = 1;
  while (y > 0) {
    if (y & 1) ret = ret * x % mod;
    x = x * x % mod;
    y >>= 1;
  }
  return ret;
}

int main() {
  int n;
  cin >> n;
  string x = input();
  string g = input();
  for (int i = 1; i < n; i++) {
    g = gcd(g, input());
  }

  long long ans = 0;
  string curr(x.size(), 0);
  for (int i = 0; i + g.size() <= x.size(); i++) {
    if (curr[i] == 0 && x[i] == 0) {
      // can't use
    } else if (curr[i] == 1 && x[i] == 0) {
      for (int j = 0; j < g.size(); j++) {
        curr[i + j] ^= g[j];
      }
    } else if (curr[i] == 0 && x[i] == 1) {
      for (int j = 0; j < g.size(); j++) {
        curr[i + j] ^= g[j];
      }
      ans += modpow(2, x.size() - i - g.size());
      ans %= mod;
    } else if (curr[i] == 1 && x[i] == 1) {
      ans += modpow(2, x.size() - i - g.size());
      ans %= mod;
    }
  }
  if (curr <= x) {
    ans++;
    ans %= mod;
  }
  
  cout << ans << endl;
}