Submission #2009030


Source Code Expand

#include <cstdio>
#include <algorithm>
#include <vector>
#include <functional>
#include <cassert>
#include <map>
#include <iostream>
#include <set>
using namespace std;

const int MOD = 1e9 + 7;

const int N = 5000001;
long long fact[N];
long long invfact[N];
long long inv[N];
void init() {
        fact[0] = fact[1] = 1;
        for (int i = 2; i < N; i ++) fact[i] = fact[i - 1] * i % MOD;
        inv[1] = 1;
        for (int i = 2; i < N; i ++) inv[i] = (MOD - MOD / i) * inv[MOD % i] % MOD;
        invfact[0] = invfact[1] = 1;
        for (int i = 2; i < N; i ++) invfact[i] = invfact[i - 1] * inv[i] % MOD;
}
long long C(long long n, long long r) {
        if (n < 0 || r < 0 || n < r) return 0;
        return fact[n] * invfact[n - r] % MOD * invfact[r] % MOD;
}

vector<int> Centroid(int root, const vector<vector<int>> &g, const vector<bool> &dead) {
        static vector<int> sz(g.size());
        int alive_cnt = 0;
        function<void (int, int)> count_alive = [&](int u, int prev) {
                alive_cnt ++;
                for (auto v : g[u]) if (v != prev && !dead[v]) {
                        count_alive(v, u);
                }
        };
        count_alive(root, -1);
        vector<int> centroid;
        function<void (int, int)> dfs = [&](int u, int prev) {
                sz[u] = 1;
                bool is_centroid = true;
                for (auto v : g[u]) if (v != prev && !dead[v]) {
                        dfs(v, u);
                        sz[u] += sz[v];
                        if (sz[v] > alive_cnt / 2) is_centroid = false;
                }
                if (alive_cnt - sz[u] > alive_cnt / 2) is_centroid = false;
                if (is_centroid) centroid.push_back(u);
        };
        dfs(root, -1);
        return centroid;
}

int main() {
        init();
        int n;
        scanf("%d", &n);
        vector<vector<int>> g(n);
        for (int i = 0; i < n - 1; i ++) {
                int a, b;
                scanf("%d%d", &a, &b);
                a --, b --;
                g[a].push_back(b);
                g[b].push_back(a);
        }
        vector<bool> dead(n);
        auto get = Centroid(0, g, dead);
        if (get.size() == 2) {
                long long ans = fact[n / 2] * fact[n / 2] % MOD;
                printf("%lld\n", ans);
                return 0;
        } else if (get.size() == 1) {
                int centroid = get[0];
                vector<int> sz(n);
                function<void (int, int)> get_size = [&](int u, int prev) {
                        sz[u] = 1;
                        for (auto v : g[u]) if (v != prev) {
                                get_size(v, u);
                                sz[u] += sz[v];
                        }
                };
                get_size(centroid, -1);
                vector<int> subtrees;
                for (auto v : g[centroid]) subtrees.push_back(sz[v]);
                int k = (int) subtrees.size();
                vector<vector<long long>> dp(k + 1, vector<long long> (n + 1, 0));
                dp[0][1] = 1;
                for (int i = 0; i < k; i ++) {
                        int num = subtrees[i];
                        for (int j = 0; j <= n - num; j ++) {
                                for (int l = 0; l <= num; l ++) {
                                        if (l & 1) {
                                                (dp[i + 1][j + num - l] -= dp[i][j] * C(num, l) % MOD * fact[num] % MOD * invfact[num - l] % MOD) %= MOD;
                                        } else {
                                                (dp[i + 1][j + num - l] += dp[i][j] * C(num, l) % MOD * fact[num] % MOD * invfact[num - l] % MOD) %= MOD;
                                        }
                                }
                        }
                }
                long long ans = 0;
                for (int i = 0; i <= n; i ++) {
                        (ans += dp[k][i] * fact[i] % MOD) %= MOD;
                }
                ans = ((ans % MOD) + MOD) % MOD;
                printf("%lld\n", ans);
        } else {
                printf("%d\n", 1 << 20);
        }
        return 0;
}

Submission Info

Submission Time
Task F - Squirrel Migration
User KokiYmgch
Language C++14 (GCC 5.4.1)
Score 800
Code Size 4275 Byte
Status AC
Exec Time 1154 ms
Memory 313344 KB

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:59:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d", &n);
                        ^
./Main.cpp:63:38: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
                 scanf("%d%d", &a, &b);
                                      ^

Judge Result

Set Name Sample All
Score / Max Score 0 / 0 800 / 800
Status
AC × 4
AC × 41
Set Name Test Cases
Sample 0_00.txt, 0_01.txt, 0_02.txt, 0_03.txt
All 0_00.txt, 0_01.txt, 0_02.txt, 0_03.txt, 1_00.txt, 1_01.txt, 1_02.txt, 1_03.txt, 1_04.txt, 1_05.txt, 1_06.txt, 1_07.txt, 1_08.txt, 1_09.txt, 1_10.txt, 1_11.txt, 1_12.txt, 1_13.txt, 1_14.txt, 1_15.txt, 1_16.txt, 1_17.txt, 1_18.txt, 1_19.txt, 1_20.txt, 1_21.txt, 1_22.txt, 1_23.txt, 1_24.txt, 1_25.txt, 1_26.txt, 1_27.txt, 1_28.txt, 1_29.txt, 1_30.txt, 1_31.txt, 1_32.txt, 1_33.txt, 1_34.txt, 1_35.txt, 1_36.txt
Case Name Status Exec Time Memory
0_00.txt AC 122 ms 117376 KB
0_01.txt AC 122 ms 117376 KB
0_02.txt AC 121 ms 117376 KB
0_03.txt AC 123 ms 117504 KB
1_00.txt AC 358 ms 118144 KB
1_01.txt AC 127 ms 118144 KB
1_02.txt AC 274 ms 117760 KB
1_03.txt AC 417 ms 117888 KB
1_04.txt AC 348 ms 117888 KB
1_05.txt AC 424 ms 117888 KB
1_06.txt AC 570 ms 120576 KB
1_07.txt AC 570 ms 120576 KB
1_08.txt AC 865 ms 215552 KB
1_09.txt AC 1154 ms 313344 KB
1_10.txt AC 753 ms 215680 KB
1_11.txt AC 754 ms 215680 KB
1_12.txt AC 575 ms 121600 KB
1_13.txt AC 346 ms 117888 KB
1_14.txt AC 404 ms 117888 KB
1_15.txt AC 419 ms 118016 KB
1_16.txt AC 460 ms 118016 KB
1_17.txt AC 499 ms 118272 KB
1_18.txt AC 536 ms 118528 KB
1_19.txt AC 548 ms 119424 KB
1_20.txt AC 557 ms 120448 KB
1_21.txt AC 575 ms 120576 KB
1_22.txt AC 576 ms 122624 KB
1_23.txt AC 595 ms 127488 KB
1_24.txt AC 622 ms 137216 KB
1_25.txt AC 691 ms 156800 KB
1_26.txt AC 699 ms 165632 KB
1_27.txt AC 761 ms 182656 KB
1_28.txt AC 859 ms 215168 KB
1_29.txt AC 122 ms 117376 KB
1_30.txt AC 122 ms 117376 KB
1_31.txt AC 123 ms 117760 KB
1_32.txt AC 128 ms 117760 KB
1_33.txt AC 123 ms 117760 KB
1_34.txt AC 123 ms 117760 KB
1_35.txt AC 123 ms 117760 KB
1_36.txt AC 129 ms 117760 KB