//////////////////////////////////////////////////////////////////////////////// // Give me AC!!! // //////////////////////////////////////////////////////////////////////////////// #include #include #include #include #include #include #include using namespace std; namespace mp = boost::multiprecision; using namespace mp; using ull = __int128; using ll = long long; using cll = cpp_int; using Graph = vector>; #define coutY cout<<"YES"< a(b) #define vl(a,b) vector a(b) #define vs(a,b) vector a(b) #define vll(a,b,c) vector> a(b, vector(c)); #define intque(a) queue a; #define llque(a) queue a; #define intque2(a) priority_queue, greater> a; #define llque2(a) priority_queue, greater> a; #define pushback(a,b) a.push_back(b) #define mapii(M1) map M1; #define cou(v,x) count(v.begin(), v.end(), x) #define mapll(M1) map M1; #define mapls(M1) map M1; #define mapsl(M1) map M1; #define twolook(a,l,r,x) lower_bound(a+l, a+r, x) - a #define sor(a) sort(a.begin(), a.end()) #define rever(a) reverse(a.begin(),a.end()) #define rep(i,a) for(ll i=0;i>n[i] #define vcout(n) for(ll i=0;i>n[i][j] const ll mod = 1000000007; const ll MOD = 1000000007; constexpr ll MAX = 5000000; //const ll _max = 9223372036854775807; const ll _max = 1223372036854775807; ll fac[MAX],finv[MAX],inv[MAX]; // テーブルを作る前処理 void COMinit() { fac[0] = fac[1] = 1; finv[0] = finv[1] = 1; inv[1] = 1; for (int i = 2; i < MAX; i++){ fac[i] = fac[i - 1] * i % MOD; inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD; finv[i] = finv[i - 1] * inv[i] % MOD; } } // 二項係数計算 long long COM(ll n,ll k){ if (n < k) return 0; if (n < 0 || k < 0) return 0; return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD; } template< int mod > struct ModInt { int x; ModInt() : x(0) {} ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {} ModInt &operator+=(const ModInt &p) { if((x += p.x) >= mod) x -= mod; return *this; } ModInt &operator-=(const ModInt &p) { if((x += mod - p.x) >= mod) x -= mod; return *this; } ModInt &operator*=(const ModInt &p) { x = (int) (1LL * x * p.x % mod); return *this; } ModInt &operator/=(const ModInt &p) { *this *= p.inverse(); return *this; } ModInt operator-() const { return ModInt(-x); } ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; } ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; } ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; } ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; } bool operator==(const ModInt &p) const { return x == p.x; } bool operator!=(const ModInt &p) const { return x != p.x; } ModInt inverse() const { int a = x, b = mod, u = 1, v = 0, t; while(b > 0) { t = a / b; swap(a -= t * b, b); swap(u -= t * v, v); } return ModInt(u); } ModInt pow(int64_t n) const { ModInt ret(1), mul(x); while(n > 0) { if(n & 1) ret *= mul; mul *= mul; n >>= 1; } return ret; } friend ostream &operator<<(ostream &os, const ModInt &p) { return os << p.x; } friend istream &operator>>(istream &is, ModInt &a) { int64_t t; is >> t; a = ModInt< mod >(t); return (is); } static int get_mod() { return mod; } }; using mint = ModInt< mod >; int modPow(long long a, long long n, long long p) { if (n == 0) return 1; // 0乗にも対応する場合 if (n == 1) return a % p; if (n % 2 == 1) return (a * modPow(a, n - 1, p)) % p; long long t = modPow(a, n / 2, p); return (t * t) % p; } ll clocks(ll a,ll b,ll c){ return a*3600+b*60+c; } ll divup(ll b,ll d){ if(b%d==0){ return b/d; } else{ return b/d+1; } } struct UnionFind { vector par; // par[i]:iの親の番号 (例) par[3] = 2 : 3の親が2 UnionFind(int N) : par(N) { //最初は全てが根であるとして初期化 for(int i = 0; i < N; i++) par[i] = i; } int root(int x) { // データxが属する木の根を再帰で得る:root(x) = {xの木の根} if (par[x] == x) return x; return par[x] = root(par[x]); } void unite(int x, int y) { // xとyの木を併合 int rx = root(x); //xの根をrx int ry = root(y); //yの根をry if (rx == ry) return; //xとyの根が同じ(=同じ木にある)時はそのまま par[rx] = ry; //xとyの根が同じでない(=同じ木にない)時:xの根rxをyの根ryにつける } bool same(int x, int y) { // 2つのデータx, yが属する木が同じならtrueを返す int rx = root(x); int ry = root(y); return rx == ry; } }; struct Edge { int to; // 辺の行き先 int weight; // 辺の重み Edge(int t, int w) : to(t), weight(w) { } }; using Graphw = vector>; ll zero(ll a){ return max(ll(0),a); } template< typename T > struct FormalPowerSeries : vector< T > { using vector< T >::vector; using P = FormalPowerSeries; using MULT = function< P(P, P) >; static MULT &get_mult() { static MULT mult = nullptr; return mult; } static void set_fft(MULT f) { get_mult() = f; } void shrink() { while(this->size() && this->back() == T(0)) this->pop_back(); } P operator+(const P &r) const { return P(*this) += r; } P operator+(const T &v) const { return P(*this) += v; } P operator-(const P &r) const { return P(*this) -= r; } P operator-(const T &v) const { return P(*this) -= v; } P operator*(const P &r) const { return P(*this) *= r; } P operator*(const T &v) const { return P(*this) *= v; } P operator/(const P &r) const { return P(*this) /= r; } P operator%(const P &r) const { return P(*this) %= r; } P &operator+=(const P &r) { if(r.size() > this->size()) this->resize(r.size()); for(int i = 0; i < r.size(); i++) (*this)[i] += r[i]; return *this; } P &operator+=(const T &r) { if(this->empty()) this->resize(1); (*this)[0] += r; return *this; } P &operator-=(const P &r) { if(r.size() > this->size()) this->resize(r.size()); for(int i = 0; i < r.size(); i++) (*this)[i] -= r[i]; shrink(); return *this; } P &operator-=(const T &r) { if(this->empty()) this->resize(1); (*this)[0] -= r; shrink(); return *this; } P &operator*=(const T &v) { const int n = (int) this->size(); for(int k = 0; k < n; k++) (*this)[k] *= v; return *this; } P &operator*=(const P &r) { if(this->empty() || r.empty()) { this->clear(); return *this; } assert(get_mult() != nullptr); return *this = get_mult()(*this, r); } P &operator%=(const P &r) { return *this -= *this / r * r; } P operator-() const { P ret(this->size()); for(int i = 0; i < this->size(); i++) ret[i] = -(*this)[i]; return ret; } P &operator/=(const P &r) { if(this->size() < r.size()) { this->clear(); return *this; } int n = this->size() - r.size() + 1; return *this = (rev().pre(n) * r.rev().inv(n)).pre(n).rev(n); } P pre(int sz) const { return P(begin(*this), begin(*this) + min((int) this->size(), sz)); } P operator>>(int sz) const { if(this->size() <= sz) return {}; P ret(*this); ret.erase(ret.begin(), ret.begin() + sz); return ret; } P operator<<(int sz) const { P ret(*this); ret.insert(ret.begin(), sz, T(0)); return ret; } P rev(int deg = -1) const { P ret(*this); if(deg != -1) ret.resize(deg, T(0)); reverse(begin(ret), end(ret)); return ret; } P diff() const { const int n = (int) this->size(); P ret(max(0, n - 1)); for(int i = 1; i < n; i++) ret[i - 1] = (*this)[i] * T(i); return ret; } P integral() const { const int n = (int) this->size(); P ret(n + 1); ret[0] = T(0); for(int i = 0; i < n; i++) ret[i + 1] = (*this)[i] / T(i + 1); return ret; } // F(0) must not be 0 P inv(int deg = -1) const { assert(((*this)[0]) != T(0)); const int n = (int) this->size(); if(deg == -1) deg = n; P ret({T(1) / (*this)[0]}); for(int i = 1; i < deg; i <<= 1) { ret = (ret + ret - ret * ret * pre(i << 1)).pre(i << 1); } return ret.pre(deg); } // F(0) must be 1 P log(int deg = -1) const { assert((*this)[0] == 1); const int n = (int) this->size(); if(deg == -1) deg = n; return (this->diff() * this->inv(deg)).pre(deg - 1).integral(); } P sqrt(int deg = -1) const { const int n = (int) this->size(); if(deg == -1) deg = n; if((*this)[0] == T(0)) { for(int i = 1; i < n; i++) { if((*this)[i] != T(0)) { if(i & 1) return {}; if(deg - i / 2 <= 0) break; auto ret = (*this >> i).sqrt(deg - i / 2) << (i / 2); if(ret.size() < deg) ret.resize(deg, T(0)); return ret; } } return P(deg, 0); } P ret({T(1)}); T inv2 = T(1) / T(2); for(int i = 1; i < deg; i <<= 1) { ret = (ret + pre(i << 1) * ret.inv(i << 1)) * inv2; } return ret.pre(deg); } // F(0) must be 0 P exp(int deg = -1) const { assert((*this)[0] == T(0)); const int n = (int) this->size(); if(deg == -1) deg = n; P ret({T(1)}); for(int i = 1; i < deg; i <<= 1) { ret = (ret * (pre(i << 1) + T(1) - ret.log(i << 1))).pre(i << 1); } return ret.pre(deg); } P pow(int64_t k, int deg = -1) const { const int n = (int) this->size(); if(deg == -1) deg = n; for(int i = 0; i < n; i++) { if((*this)[i] != T(0)) { T rev = T(1) / (*this)[i]; P C(*this * rev); P D(n - i); for(int j = i; j < n; j++) D[j - i] = C[j]; D = (D.log() * k).exp() * (*this)[i].pow(k); P E(deg); if(i * k > deg) return E; auto S = i * k; for(int j = 0; j + S < deg && j < D.size(); j++) E[j + S] = D[j]; return E; } } return *this; } T eval(T x) const { T r = 0, w = 1; for(auto &v : *this) { r += w * v; w *= x; } return r; } }; //aはbの何乗以下かを満たす数の内最大の物,(a,10)はaの桁数 ll expless(ll a,ll b){ ll k=0; ll o=1; while(a>=o){ k++; o=o*b; } return k; } //aをb進法で表す ll base(ll a,ll b){ ll ans=0; ll k; while(a>0){ k=a%b; ans+=k; a=a/b; } return ans; } //b進法のaを10進法に直す ll tenbase(ll a,ll b){ ll c=expless(a,10); ll ans=0; ll k=1; for(int i=0;i > prime_factorize(long long N) { vector > res; for (long long a = 2; a * a <= N; ++a) { if (N % a != 0) continue; long long ex = 0; // 指数 // 割れる限り割り続ける while (N % a == 0) { ++ex; N /= a; } // その結果を push res.push_back({a, ex}); } // 最後に残った数について if (N != 1) res.push_back({N, 1}); return res; } ll atll(ll a,ll b){ b++; ll c=expless(a,10); ll d=c-b; ll f=1; for(int i=0;i vector smallest_prime_factors(T n) { vector spf(n + 1); for (int i = 0; i <= n; i++) spf[i] = i; for (T i = 2; i * i <= n; i++) { // 素数だったら if (spf[i] == i) { for (T j = i * i; j <= n; j += i) { // iを持つ整数かつまだ素数が決まっていないなら if (spf[j] == j) { spf[j] = i; } } } } return spf; } vector> factolization(ll x, vector &spf) { vector> ret; ll p; ll z; while (x != 1) { p=(spf[x]); z=0; while(x%p==0){ z++; x /= p; } ret.push_back({p, z}); } return ret; } ll f(ll a,ll b){ if(b!=0){ return (a-b+1)*modPow(a+1,b-1,MOD)%MOD; } else{ return 1; } } int main(){ COMinit(); ll n,m; cin>>n>>m; string s; cin>>s; ll cnt=0; mint ans=0; ll count=0; mint tmp=0; vector xo; ll x=0; for(ll i=0;i=1){ tmp-=m*f(n-1,i+m); } if(n-m-i>=2){ for(int j=0;j<=m-2;++j){ tmp+=(((m-1-j)*f(n-2-j,i+m-j))%mod*f(j,j))%mod*COM(m+i,j)%mod; } } ans=ans+(((tmp)*(n-m+1))*modPow(n,n-m-i,mod)); } cout< table(max(l+r-1,1LL),0); for(int i=0;i=1){ for(int j=0;j<=l-1;j++){ tmp2-=mint(f((n-m+l+r)-(1+j),(i+l+r)-j)*f(j,j)*modPow(i+l+r,j,mod)); } for(int j=0;j<=r-1;j++){ tmp2-=mint(mint(f((n-m+l+r)-(1+j),(i+l+r)-j)*f(j,j))*modPow(i+l+r,j,mod)); } } if(n-m-i>=2){ for(int j=0;j<=l+r-2;j++){ tmp2+=mint(f((n-m+l+r)-(2+j),(i+l+r)-j)*table[j]*modPow(i+l+r,j,mod)); } } ans+=mint(mint(mint(mint(tmp*tmp2)*COM(i+l+r+cnt,cnt))*(n-m+1))*modPow(n,n-i-cnt-l-r,mod)); // cout<