結果
| 問題 | No.2237 Xor Sum Hoge |
| コンテスト | |
| ユーザー |
 qwewe
|
| 提出日時 | 2025-05-14 12:58:44 |
| 言語 | C++17 (gcc 13.3.0 + boost 1.89.0) |
| 結果 |
AC
|
| 実行時間 | 1,528 ms / 10,000 ms |
| コード長 | 9,542 bytes |
| 記録 | |
| コンパイル時間 | 1,973 ms |
| コンパイル使用メモリ | 95,344 KB |
| 実行使用メモリ | 10,624 KB |
| 最終ジャッジ日時 | 2025-05-14 13:00:34 |
| 合計ジャッジ時間 | 30,405 ms |
|
ジャッジサーバーID （参考情報） |
judge1 / judge2 |
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| ファイルパターン | 結果 |
|---|---|
| sample | AC * 3 |
| other | AC * 32 |
ソースコード
#include <iostream>
#include <vector>
#include <numeric>
#include <cmath> // Included for completeness, LOGP calculation done manually
// Use long long for intermediate calculations involving large numbers or multiplication
using ll = long long;
// Define the modulus for calculations
const int MOD = 998244353;
// Modular exponentiation: computes (base^exp) % MOD
ll power(ll base, ll exp) {
ll res = 1;
base %= MOD;
while (exp > 0) {
if (exp % 2 == 1) res = (res * base) % MOD;
base = (base * base) % MOD;
exp /= 2;
}
return res;
}
// Modular inverse using Fermat's Little Theorem: computes n^(MOD-2) % MOD
// Assumes MOD is prime and n is not a multiple of MOD.
ll modInverse(ll n) {
// Handle n=0 case if necessary, though it shouldn't occur for factorials or FFT size P
if (n == 0) return 0;
return power(n, MOD - 2);
}
// Namespace for Number Theoretic Transform (NTT) implementation
namespace NTT {
// Define maximum possible FFT size needed.
// Max N=60000 -> product degree 2N=120000 -> requires FFT size P >= 120001.
// Smallest power of 2 is 2^17 = 131072.
const int MAX_LEN = 1 << 17;
ll G = 3; // Primitive root modulo 998244353
ll W[MAX_LEN]; // Stores powers of primitive root omega
ll invW[MAX_LEN]; // Stores powers of inverse primitive root omega^-1
int rev[MAX_LEN]; // Stores bit reversal permutation indices
bool roots_precomputed = false; // Flag to ensure roots are computed only once
// Precompute powers of primitive roots for FFT up to size N_fft
// N_fft must be a power of 2, and should be MAX_LEN for general use
void precompute_roots(int N_fft) {
if (roots_precomputed) return;
ll WN = power(G, (MOD - 1) / N_fft); // N_fft-th primitive root of unity
ll invWN = modInverse(WN); // Inverse root
W[0] = invW[0] = 1;
for (int i = 1; i < N_fft; ++i) {
W[i] = (W[i - 1] * WN) % MOD;
invW[i] = (invW[i - 1] * invWN) % MOD;
}
roots_precomputed = true;
}
// Precompute bit reversal indices for a specific FFT size P
// P must be a power of 2. LOGP is log2(P).
void precompute_bitrev(int P, int LOGP) {
// Ensure P is within bounds for the rev array
if (P > MAX_LEN) { /* Handle error or resize */ return; }
for (int i = 0; i < P; ++i) {
rev[i] = 0;
for (int j = 0; j < LOGP; ++j) {
if ((i >> j) & 1) {
rev[i] |= (1 << (LOGP - 1 - j));
}
}
}
}
// Perform NTT or inverse NTT in place on vector `a` of size P
// P must be a power of 2. `invert` flag determines direction.
void ntt(std::vector<ll>& a, int P, bool invert) {
// Ensure vector `a` has size at least P, padding with zeros if necessary
if (a.size() < P) a.resize(P, 0);
// Apply bit reversal permutation using precomputed `rev` array for size P
for (int i = 0; i < P; ++i) {
if (i < rev[i]) {
std::swap(a[i], a[rev[i]]);
}
}
// Select appropriate roots (W or invW) based on `invert` flag
ll* roots = invert ? invW : W;
// The roots W/invW were precomputed for MAX_LEN. We need to use the correct step size.
for (int len = 2; len <= P; len <<= 1) { // Iterate through transform lengths
int half_len = len >> 1;
// Calculate step size into the precomputed roots array (size MAX_LEN)
int root_step = MAX_LEN / len;
for (int i = 0; i < P; i += len) { // Iterate through blocks
ll w_idx = 0; // Index into the W/invW array
for (int j = 0; j < half_len; ++j) { // Butterfly operations within block
ll u = a[i + j];
// Multiply with appropriate power of root of unity
ll v = (a[i + j + half_len] * roots[w_idx]) % MOD;
// Combine results
a[i + j] = (u + v) % MOD;
a[i + j + half_len] = (u - v + MOD) % MOD; // Add MOD to ensure non-negative result
// Move to the next required root power
w_idx = (w_idx + root_step); // No need for % MAX_LEN if indices stay within bounds
}
}
}
// If inverse NTT, scale result by 1/P
if (invert) {
ll invP = modInverse(P);
for (int i = 0; i < P; ++i) {
a[i] = (a[i] * invP) % MOD;
}
}
}
}
// Maximum value for problem parameter N, used for array sizing
const int MAXN_PARAM = 60000 + 5;
// Precomputed factorials and inverse factorials for combinations
ll fact[MAXN_PARAM];
ll invFact[MAXN_PARAM];
// Precompute factorials and their modular inverses up to N_max
void precompute_combinations(int N_max) {
// Ensure N_max does not exceed array bounds
if (N_max >= MAXN_PARAM) N_max = MAXN_PARAM - 1;
fact[0] = 1;
for (int i = 1; i <= N_max; ++i) {
fact[i] = (fact[i - 1] * i) % MOD;
}
invFact[N_max] = modInverse(fact[N_max]);
for (int i = N_max - 1; i >= 0; --i) {
invFact[i] = (invFact[i + 1] * (i + 1)) % MOD;
}
}
// Compute combinations nCk mod MOD using precomputed values
ll combinations(int n, int k) {
if (k < 0 || k > n) {
return 0; // Invalid k
}
// Ensure n is within the precomputed range
if (n >= MAXN_PARAM) { /* handle error */ return 0; }
return (((fact[n] * invFact[k]) % MOD) * invFact[n - k]) % MOD;
}
int main() {
// Use fast I/O operations
std::ios_base::sync_with_stdio(false);
std::cin.tie(NULL);
int N; // Problem parameter N: length of sequence A
unsigned long long B_val, C_val; // Target sum B and XOR sum C
std::cin >> N >> B_val >> C_val;
// Precompute factorials and inverse factorials needed for combinations up to N
precompute_combinations(N);
// Determine required FFT size P: smallest power of 2 such that P > 2N
// The product polynomial degree can be up to N + N = 2N.
int P = 1;
int LOGP = 0;
while (P <= 2 * N) {
P <<= 1;
LOGP++;
}
// Precompute NTT roots for the maximum possible FFT size (MAX_LEN)
NTT::precompute_roots(NTT::MAX_LEN);
// Precompute bit reversal indices specifically for the calculated FFT size P
NTT::precompute_bitrev(P, LOGP);
// Initialize DP state vector `dp_coeffs`. dp_coeffs[c] stores dp[k][c].
// Initially, dp[0][0] = 1 (1 way to have carry 0 before processing bit 0).
std::vector<ll> dp_coeffs(N + 1, 0);
dp_coeffs[0] = 1;
// Iterate through bits k from 0 to 59 (since B, C < 2^60)
for (int k = 0; k < 60; ++k) {
// Extract k-th bits of B and C
unsigned long long B_k = (B_val >> k) & 1;
unsigned long long C_k = (C_val >> k) & 1;
// Prepare the polynomial representing current DP states for NTT (size P)
std::vector<ll> current_dp(P, 0);
// Determine required parity for carry c_k: c_k % 2 == B_k ^ C_k
ll required_carry_parity = B_k ^ C_k;
// Filter DP states based on carry parity: copy only valid states
for (int c = 0; c <= N; ++c) {
if (dp_coeffs[c] != 0) { // Consider only reachable states (non-zero counts)
if ((c % 2) == required_carry_parity) {
current_dp[c] = dp_coeffs[c];
}
}
}
// Prepare the polynomial representing combinations for NTT (size P)
// P_N(y) = sum_{x=0..N, x%2 == C_k} C(N, x) * y^x
std::vector<ll> poly_comb(P, 0);
ll required_x_parity = C_k; // x_k must have parity C_k
for (int x = 0; x <= N; ++x) {
if ((x % 2) == required_x_parity) {
poly_comb[x] = combinations(N, x);
}
}
// Transform both polynomials to frequency domain using NTT
NTT::ntt(current_dp, P, false);
NTT::ntt(poly_comb, P, false);
// Perform pointwise multiplication in frequency domain
std::vector<ll> H_coeffs_ntt(P); // Stores NTT of the product polynomial H(y)
for (int i = 0; i < P; ++i) {
H_coeffs_ntt[i] = (current_dp[i] * poly_comb[i]) % MOD;
}
// Transform product back to coefficient domain using inverse NTT
NTT::ntt(H_coeffs_ntt, P, true);
// Calculate coefficients for the next DP state dp[k+1] from H(y) coefficients
std::vector<ll> new_dp_coeffs(N + 1, 0); // Stores dp[k+1][j] values
for (int j = 0; j <= N; ++j) { // Index j represents the next carry c_{k+1}
// Check bounds: indices 2j and 2j+1 must be less than P
ll h_2j = (2 * j < P) ? H_coeffs_ntt[2 * j] : 0;
ll h_2j_plus_1 = (2 * j + 1 < P) ? H_coeffs_ntt[2 * j + 1] : 0;
// Update rule: dp[k+1][j] = h_{2j} + h_{2j+1}
new_dp_coeffs[j] = (h_2j + h_2j_plus_1) % MOD;
// Ensure result is non-negative modulo MOD (though addition should preserve non-negativity)
// if (new_dp_coeffs[j] < 0) new_dp_coeffs[j] += MOD;
}
// Update DP state vector for the next bit iteration
dp_coeffs = new_dp_coeffs;
}
// The final answer is dp[60][0]: number of ways resulting in carry 0 after processing all 60 bits.
std::cout << dp_coeffs[0] << std::endl;
return 0;
}