#include #define rep(i, a, n) for(int i = a; i < (n); i++) using namespace std; using ll = long long; using P = pair; const int INF = 1001001001; const ll LINF = 1001002003004005006ll; //const int mod = 1000000007; //const int mod = 998244353; //NNT template struct NTT { vector rev, rts; int base, max_base, root; NTT(): base(1), rev{0, 1}, rts{0, 1} { assert(mod >= 3 && mod&1); auto tmp = mod-1; max_base = 0; while (tmp%2 == 0) { tmp >>= 1; max_base++; } root = 2; while (mod_pow(root, (mod-1)>>1) == 1) root++; assert(mod_pow(root, mod-1) == 1); root = mod_pow(root, (mod-1)>>max_base); } inline int mod_pow(int x, int n) { int res = 1; while (n > 0) { if (n&1) res = mul(res, x); x = mul(x, x); n >>= 1; } return res; } inline int inverse(int x) { return mod_pow(x, mod-2); } inline unsigned add(unsigned x, unsigned y) { x += y; if (x >= mod) x -= mod; return x; } inline unsigned mul(unsigned a, unsigned b) { return 1ull*a*b%(unsigned long long)mod; } void ensure_base(int nbase) { if (nbase <= base) return; rev.resize(1<>1]>>1)+((i&1)<<(nbase-1)); assert(nbase <= max_base); while (base < nbase) { int z = mod_pow(root, 1<<(max_base-1-base)); for (int i = 1<<(base-1); i < (1<& a) { const int n = (int)a.size(); assert((n&(n-1)) == 0); int zeros = __builtin_ctz(n); ensure_base(zeros); int shift = base - zeros; for (int i = 0; i < n; i++) if (i < (rev[i]>>shift)) swap(a[i], a[rev[i]>>shift]); for (int k = 1; k < n; k <<= 1) { for (int i = 0; i < n; i += 2*k) { for (int j = 0; j < k; j++) { int z = mul(a[i+j+k], rts[j+k]); a[i+j+k] = add(a[i+j], mod-z); a[i+j] = add(a[i+j], z); } } } } vector multiply(vector a, vector b) { int need = (int)a.size() + (int)b.size() - 1; int nbase = 1; while ((1< rts={{0,0},{1,0}}; vector rev={0,1}; const double PI=acosl(-1.0); void ensure_base(int nbase){ if(nbase<=base) return; rev.resize(1<>1]>>1)+((i&1)<<(nbase-1)); rts.resize(1< &a,int n=-1){ if(n == -1) n = (int)a.size(); assert((n&(n-1))==0); int zeros=__builtin_ctz(n); ensure_base(zeros); int shift=base-zeros; for(int i=0;i>shift)) swap(a[i],a[rev[i]>>shift]); for(int k=1;k fa; template vector multiply(const vector &a,const vector &b){ int need=(int)a.size()+b.size()-1; int nbase=0; while((1<(int)fa.size()) fa.resize(sz); for(int i=0;i>1);i++){ int j=(sz-i)&(sz-1); num z=(fa[j]*fa[j]-conj(fa[i]*fa[i]))*r; if(i!=j) fa[j]=(fa[i]*fa[i]-conj(fa[j]*fa[j]))*r; fa[i]=z; } fft(fa,sz); vector res(need); for(int i=0;i> n >> x; vector a(n); rep(i, 0, n) cin >> a[i]; vector cnt(100005); rep(i, 0, n) cnt[a[i]]++; NTT<> ntt; auto f = ntt.multiply(cnt, cnt); cout << f[x] << endl; return 0; }