#include "bits/stdc++.h"
using namespace std;
void abc() {cout << endl;}
template <typename T, typename ...U> void abc(T a, U ...b) {
cout << a << ' ', abc(b...);
}
template <typename T> void printv(T l, T r) {
while (l != r) cout << *l << " \n"[++l == r];
}
template <typename A, typename B> istream& operator >> (istream& o, pair<A, B> &a) {
return o >> a.first >> a.second;
}
template <typename A, typename B> ostream& operator << (ostream& o, pair<A, B> a) {
return o << '(' << a.first << ", " << a.second << ')';
}
template <typename T> ostream& operator << (ostream& o, vector<T> a) {
bool is = false;
for (T i : a) {o << (is ? ' ' : '{'), is = true, o << i;}
return o << '}';
}
#ifdef local
#define test(args...) abc("[" + string(#args) + "]", args)
#else
#define test(args...) void(0)
#endif
using ll = long long;
int loc[4005];
int lpar[4005], rpar[4005];
ll dp[4005][4005]; // at node i, need j balls from above
int above[4005]; //exclusive
int below[4005]; //inclusive
int sz[4005];
const ll MOD = 1e9 + 7;
ll factorial[4005];
ll inverse[4005];
ll choose(int a, int b) {
if (a < b) return 0;
return ((factorial[a] % MOD * inverse[b] % MOD) % MOD) * (inverse[a - b]) % MOD;
}
void dfs(int node, int par = -1, bool left = true) {
below[node] = loc[node];
sz[node] = 1;
if (lpar[node]) {
above[lpar[node]] = above[node] + loc[node];
dfs(lpar[node], node, true);
below[node] += below[lpar[node]];
sz[node] += sz[lpar[node]];
}
if (rpar[node]) {
above[rpar[node]] = above[node] + loc[node];
dfs(rpar[node], node, false);
below[node] += below[rpar[node]];
sz[node] += sz[rpar[node]];
}
if (sz[node] < below[node]) {
cout << 0 << '\n';
exit(0);
}
// if (lpar[node] ==0 && rpar[node] == 0) {
// if (loc[node] > 1) {
// cout << 0 << "\n";
// exit(0);
// }
//
// if (lpar[node] || rpar[node]) {
// dp[node][0] = 1;
// } else {
// dp[node][1] = 1;
// }
//
// return;
// }
int lc = lpar[node];
int rc = rpar[node];
int leftsz = sz[lc] - below[lc];
int rightsz = sz[rc] - below[rc];
int lefttaken = below[lc];
int righttaken = below[rc];
int space = sz[node] - lefttaken - righttaken;
if (!left) {
swap(lc, rc);
swap(leftsz, rightsz);
swap(lefttaken, righttaken);
}
// the root is somewhere else
{
for (int take = 0; take <= leftsz && take <= loc[node]; take++) {
int takeo = loc[node] - take;
if (takeo > rightsz) continue;
for (int i = 0; i <= above[node] && i + loc[node] <= space; i++) {
int amtleft = min(leftsz, take + i);
int remain = take + i - amtleft;
int amtright = min(rightsz, remain + takeo);
if (amtleft + amtright < loc[node]) continue;
ll constant = 1;
if (loc[node] + i == amtleft + amtright + 1) {
constant = choose(loc[node], take) % MOD;
constant = (constant * choose(i, amtleft - take) % MOD * choose(i - (amtleft - take), 1));
} else {
constant = choose(loc[node], take) % MOD;
constant = (constant % MOD * choose(i, amtleft - take));
}
dp[node][i] = (dp[node][i] + ((dp[lc][amtleft] * dp[rc][amtright]) % MOD) * constant) % MOD;
}
}
}
// take root with itself
{
for (int take = 0; take <= leftsz && take < loc[node]; take++) {
int takeo = loc[node] - take - 1;
if (takeo > rightsz) continue;
for (int i = 0; i <= above[node] && i + loc[node] <= space; i++) {
int amtleft = min(leftsz, take + i);
int remain = take + i - amtleft;
int amtright = min(rightsz, remain + takeo);
if (amtleft + amtright + 1 < loc[node]) continue;
if (i + loc[node] != space) {
continue;
}
ll constant;
if (loc[node] + i == amtleft + amtright + 1) {
constant = (choose(loc[node], take) * choose(loc[node] - take, takeo)) % MOD;
constant = (constant * choose(i, amtleft - take)) % MOD;
} else {
constant = choose(loc[node], take) % MOD;
constant = (constant * choose(i, amtleft - take));
}
dp[node][i] = (dp[node][i] + ((dp[lc][amtleft] * dp[rc][amtright]) % MOD) * constant) % MOD;
}
}
}
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
// freopen("", "r", stdin);
// freopen("", "w", stdout);
int n, k; cin >> n >> k;
factorial[0] = 1;
for (int i = 1; i <= 4004; i++) {
factorial[i] = (factorial[i - 1] * i) % MOD;
}
inverse[0] = 1;
inverse[1] = 1;
for (int i = 2; i <= 4004; i++) {
inverse[i] = MOD - (MOD / i) * inverse[MOD % i] % MOD;
}
if (k > n) {
cout << "0\n";
exit(0);
}
for (int i = 1; i <= k; i++) {
int t; cin >> t;
loc[t]++;
}
for (int i = 1; i <= n; i++) cin >> lpar[i] >> rpar[i];
dp[0][0] = 1;
dfs(1);
cout << dp[1][0] % MOD << "\n";
}
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
0 ms |
340 KB |
Output is correct |
| 2 |
Correct |
1 ms |
340 KB |
Output is correct |
| 3 |
Correct |
1 ms |
340 KB |
Output is correct |
| 4 |
Correct |
0 ms |
340 KB |
Output is correct |
| 5 |
Correct |
1 ms |
340 KB |
Output is correct |
| 6 |
Correct |
0 ms |
340 KB |
Output is correct |
| 7 |
Correct |
1 ms |
468 KB |
Output is correct |
| 8 |
Incorrect |
1 ms |
340 KB |
Output isn't correct |
| 9 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
11 ms |
17492 KB |
Output is correct |
| 2 |
Incorrect |
55 ms |
32580 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
11 ms |
16724 KB |
Output is correct |
| 2 |
Correct |
14 ms |
17528 KB |
Output is correct |
| 3 |
Correct |
14 ms |
16620 KB |
Output is correct |
| 4 |
Incorrect |
12 ms |
16692 KB |
Output isn't correct |
| 5 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
0 ms |
340 KB |
Output is correct |
| 2 |
Correct |
1 ms |
340 KB |
Output is correct |
| 3 |
Correct |
1 ms |
340 KB |
Output is correct |
| 4 |
Correct |
0 ms |
340 KB |
Output is correct |
| 5 |
Correct |
1 ms |
340 KB |
Output is correct |
| 6 |
Correct |
0 ms |
340 KB |
Output is correct |
| 7 |
Correct |
1 ms |
468 KB |
Output is correct |
| 8 |
Incorrect |
1 ms |
340 KB |
Output isn't correct |
| 9 |
Halted |
0 ms |
0 KB |
- |
