mirror of
https://github.com/Kiritow/OJ-Problems-Source.git
synced 2024-03-22 13:11:29 +08:00
122 lines
3.0 KiB
C++
122 lines
3.0 KiB
C++
#pragma comment(linker, "/STACK:102400000,102400000")
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#include <iostream>
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#include <cstdio>
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#include <algorithm>
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#include <string>
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#include <cmath>
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#include <cstring>
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#include <queue>
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#include <set>
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#include <map>
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#include <vector>
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using namespace std;
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template <class T>
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inline bool rd(T &ret) {
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char c; int sgn;
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if (c = getchar(), c == EOF) return 0;
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while (c != '-' && (c<'0' || c>'9')) c = getchar();
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sgn = (c == '-') ? -1 : 1;
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ret = (c == '-') ? 0 : (c - '0');
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while (c = getchar(), c >= '0'&&c <= '9') ret = ret * 10 + (c - '0');
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ret *= sgn;
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return 1;
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}
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template <class T>
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inline void pt(T x) {
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if (x < 0) {
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putchar('-');
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x = -x;
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}
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if (x > 9) pt(x / 10);
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putchar(x % 10 + '0');
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}
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typedef pair<int, int> pii;
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typedef long long ll;
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const int N = 1005;
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const int mod = 1e9 + 7;
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const int inf = 1e9;
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int Pow(int x, int y) {
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int ans = 1;
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while (y) {
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if (y & 1)ans = (ll)ans*x%mod;
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y >>= 1;
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x = (ll)x*x%mod;
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}return ans;
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}
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vector<int>G[N];
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int n, k;
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int dp[N][N], siz[N], lef[N];
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int A[N];
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int mul(int x, int y) {
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x = (ll)x*y%mod;
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return x;
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}
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inline void add(int &x, int y) {
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x += y; if (x >= mod)x -= mod;
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}
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inline void sub(int &x, int y) {
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x -= y; if (x < 0)x += mod;
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}
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inline void dv(int &x, int y) {
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x = (ll)x*Pow(y, mod - 2) % mod;
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}
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int g[N];
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void dfs(int u, int fa) {
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siz[u] = 1; lef[u] = 0;
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for (auto v : G[u]) {
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if (v == fa)continue;
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dfs(v, u);
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siz[u] += siz[v];
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}
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if (siz[u] == 1) {
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dp[u][0] = 0; dp[u][1] = 1;
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lef[u] = 1;
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return;
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}
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dp[u][0] = 1;
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int x1 = A[siz[u] - 1], x2 = A[siz[u]];
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siz[u] = 0;
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for (auto v : G[u]) {
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if (v == fa)continue;
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for (int i = lef[u] + lef[v]; i <= min(k, siz[u] + siz[v]); i++)g[i] = 0;
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for (int i = lef[u]; i <= min(k, siz[u]); i++)
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{
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for (int j = lef[v]; j <= min(k, siz[v]) && i + j <= k; j++)
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{
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add(g[i + j], mul(dp[v][j], dp[u][i]));
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}
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}
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for (int i = lef[u] + lef[v]; i <= min(k, siz[u] + siz[v]); i++)dp[u][i] = g[i];
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siz[u] += siz[v];
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lef[u] += lef[v];
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dv(x1, A[siz[v]]);
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dv(x2, A[siz[v]]);
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}
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siz[u]++;
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sub(x2, x1);
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for (int i = min(siz[u], k); i >= lef[u]; i--) {
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int tmp = 0;
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add(tmp, mul(dp[u][i], x2));
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if (i - 1 >= lef[u])
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add(tmp, mul(dp[u][i - 1], x1));
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dp[u][i] = tmp;
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}
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}
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int main() {
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A[0] = 1;
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for (int i = 1; i < N; i++)A[i] = (ll)A[i - 1] * i%mod;
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int T, Cas = 1; rd(T);
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while (T--) {
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rd(n); rd(k);
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for (int i = 1; i <= n; i++)G[i].clear(), memset(dp[i], 0, sizeof dp[i]);
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for (int i = 1, u, v; i < n; i++) {
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rd(u); rd(v);
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G[u].push_back(v); G[v].push_back(u);
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}
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dfs(1, 1);
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printf("Case #%d: ", Cas++);
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pt(dp[1][k]); puts("");
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}
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return 0;
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}
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