#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; //#define int long long typedef long long ll; typedef unsigned long long ul; typedef unsigned int ui; constexpr ll mod = 1000000007; const ll INF = mod * mod; typedef pairP; #define stop char nyaa;cin>>nyaa; #define rep(i,n) for(int i=0;i=0;i--) #define Rep(i,sta,n) for(int i=sta;i=1;i--) #define Rep1(i,sta,n) for(int i=sta;i<=n;i++) #define all(v) (v).begin(),(v).end() typedef pair LP; typedef long double ld; typedef pair LDP; const ld eps = 1e-12; const ld pi = acos(-1.0); void chmin(int &a, int b) { a = min(a, b); } void chmax(int &a, int b) { a = max(a, b); } ll mod_pow(ll a, ll n, ll m = mod) { a %= m; ll res = 1; while (n) { if (n & 1)res = res * a%m; a = a * a%m; n >>= 1; } return res; } struct modint { ll n; modint() :n(0) { ; } modint(ll m) :n(m) { if (n >= mod)n %= mod; else if (n < 0)n = (n%mod + mod) % mod; } operator int() { return n; } }; bool operator==(modint a, modint b) { return a.n == b.n; } modint operator+=(modint &a, modint b) { a.n += b.n; if (a.n >= mod)a.n -= mod; return a; } modint operator-=(modint &a, modint b) { a.n -= b.n; if (a.n < 0)a.n += mod; return a; } modint operator*=(modint &a, modint b) { a.n = ((ll)a.n*b.n) % mod; return a; } modint operator+(modint a, modint b) { return a += b; } modint operator-(modint a, modint b) { return a -= b; } modint operator*(modint a, modint b) { return a *= b; } modint operator^(modint a, int n) { if (n == 0)return modint(1); modint res = (a*a) ^ (n / 2); if (n % 2)res = res * a; return res; } ll inv(ll a, ll p) { return (a == 1 ? 1 : (1 - p * inv(p%a, a)) / a + p); } modint operator/(modint a, modint b) { return a * modint(inv(b, mod)); } const int max_n = 1 << 18; modint fact[max_n], factinv[max_n]; void init_f() { fact[0] = modint(1); for (int i = 0; i < max_n - 1; i++) { fact[i + 1] = fact[i] * modint(i + 1); } factinv[max_n - 1] = modint(1) / fact[max_n - 1]; for (int i = max_n - 2; i >= 0; i--) { factinv[i] = factinv[i + 1] * modint(i + 1); } } modint comb(int a, int b) { if (a < 0 || b < 0 || a < b)return 0; return fact[a] * factinv[b] * factinv[a - b]; } int dx[4] = { 0,1,0,-1 }; int dy[4] = { 1,0,-1,0 }; int k; const int mn = 1000; struct edge { int to; }; using Data = vector; vector G[mn]; vector ids[mn]; vector memo[mn]; int root; Data merge(Data a, Data b) { Data res; // rep(i, a.size()) { res.push_back(a[i] * b[i]); } // return res; } Data dfs(int id, int fr) { Data res; // //initialize res.resize(k + 1, 1); // for (edge e : G[id]) { if (e.to == fr)continue; Data nex = dfs(e.to, id); // //update with edge // res = merge(res, nex); ids[id].push_back(e.to); memo[id].push_back(nex); } // //update for return modint sum = 0; rep1(i, k-1) { res[i + 1] += res[i]; } res[0] = 0; // return res; } vector par[1000]; void invdfs(int id, int fr, Data pre) { vector v; for (Data d : memo[id])v.push_back(d); if (fr >= 0)v.push_back(pre); int len = v.size(); // //calcurate id's ans par[id] = pre; // vector le(len + 1); vector ri(len + 1); // Data init_c(k+1,1); // le[0] = init_c; rep(i, len) { le[i + 1] = merge(le[i], v[i]); } ri[len] = init_c; per(i, len) { ri[i] = merge(ri[i + 1], v[i]); } rep(i, ids[id].size()) { int to = ids[id][i]; Data d = merge(le[i], ri[i + 1]); // //update for return rep1(j, k - 1)d[j + 1] += d[j]; d[0] = 0; // invdfs(to, id, d); } } void yaru() { dfs(root, -1); vector init_c(k + 1, 1); invdfs(root, -1, init_c); } modint ans = 0; modint dp[1000][1001]; void calcdfs(int id, int fr) { for (edge e : G[id]) { if (e.to == fr)continue; calcdfs(e.to, id); } rep1(i, k)dp[id][i] = 1; rep(j, ids[id].size()) { int to = ids[id][j]; rep1(i, k) { dp[id][i] *= (memo[id][j][i - 1] + dp[to][i]); } } rep1(i, k) { //cout << id << " " << i << " " << par[id][i - 1]<<" "<< dp[id][i] << "\n"; ans += par[id][i - 1] * dp[id][i]; } } void solve() { int n; cin >> n >> k; rep(i, n - 1) { int a, b; cin >> a >> b; a--; b--; G[a].push_back({ b }); G[b].push_back({ a }); } yaru(); calcdfs(0, -1); cout << ans << "\n"; } signed main() { ios::sync_with_stdio(false); cin.tie(0); //cout << fixed << setprecision(7); //init_f(); //init(); solve(); stop return 0; }