0w1

Yuki 623 fudan no modulus to tigau

Problem Description:
f:id:h0rnet:20171226165007p:plain
Given Q queries of X's, compute f(X), modulo 998244353.

Constraints:
2≤n≤50
1≤q≤50
0≤ai,bi≤i - 1
0≤xi≤998244352

Solution:
Compute each query independently, the only variant is n (relevantly small), so we can apply DP.

Code:

#include <bits/stdc++.h>

const int MOD = 998244353;

signed main() {
  std::ios::sync_with_stdio(false);
  int N;
  std::cin >> N;
  std::vector<int> T(N + 1), A(N + 1), B(N + 1);
  for (int i = 2; i <= N; ++i) {
    std::cin >> T[i] >> A[i] >> B[i];
  }
  int Q;
  std::cin >> Q;
  while (Q--) {
    int X;
    std::cin >> X;
    std::vector<int> dp(N + 1, -1);
    std::function<int(int, int)> f = [&](int n, int x) {
      if (n == 0) return 1;
      if (n == 1) return x;
      if (~dp[n]) return dp[n];
      if (T[n] == 1) return dp[n] = (f(A[n], x) + f(B[n], x)) % MOD;
      if (T[n] == 2) return dp[n] = 1LL * A[n] * f(B[n], x) % MOD;
      return dp[n] = 1LL * f(A[n], x) * f(B[n], x) % MOD;
    };
    std::cout << f(N, X) << std::endl;
  }
  return 0;
}