OJ-Problems-Source/HDOJ/5378_autoAC.cpp

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