题解

说*****简单*****那是假的
题解如下

#include <algorithm>
#include <cstdio>
using namespace std;
const long long mod = 998244353;
const int maxn = 300010;

int n, m, a;
long long A[maxn];
int gcd(int x, int y) {
    while (y) {
        x %= y;
        swap(x, y);
    }
    return x;
}

long long SG(long long x) {
    if (a == 0) return x;
    if (x < m + a) return (x / a) & 1;
    x -= 2 * a;
    long long q = x / m, r = x % m;
    if (2 * a <= m) {
        return (r % (2 * a) >= a) ? 1 : ((r >= m - a) << 1);
    }
    return r < m - a ? 0 : min(q + 1, (m - r - 1) / (m - a)) + 1;
}

int main() {
    scanf("%d %d %d", &n, &m, &a);
    int g = gcd(a, m);
    m /= g, a /= g;
    long long nim = 0;
    for (int i = 1; i <= n; i++) {
        scanf("%lld", &A[i]);
        A[i] /= g;
        nim ^= SG(A[i]);
    }
    if (nim == 0) {
        printf("0\n");
        return 0;
    }
    if (a == 0) {
        int ans = 0;
        for (int i = 1; i <= n; i++) ans += (nim ^ A[i]) < A[i];
        printf("%d\n", ans);
        return 0;
    }
    long long ans = 0;
    for (int i = 1; i <= n; i++) {
        auto get = [m, a](long long x, long long v) {
            long long l = 0, r = (x - a) / m;
            while (l <= r) {
                long long mid = (l + r) >> 1;
                if (SG((x - a) % m + mid * m) <= v) l = mid + 1;
                else r = mid - 1;
            }
            return l;
        };
        long long v = nim ^ SG(A[i]);
        ans = (ans + get(A[i], v) - get(A[i], v - 1)) % mod;
    }
    printf("%lld\n", ans);
    return 0;
}