Submission #773920

#	Time	Username	Problem	Language	Result	Execution time	Memory
773920		ParsaS	Sumtree (INOI20_sumtree)	C++17	30 / 100	304 ms	92108 KiB

Main

// In the name of God
#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define fi first
#define se second
#define mp make_pair
typedef long long ll;
const int N = 1e6 + 5, MOD = 1e9 + 7;
int n, r;
int fact[N], inv[N], f[N], c[N];
int val[N], par[N];
vector<int> adj[N];

int binpow(int a, int b) {
    return b ? 1LL * binpow(1LL * a * a % MOD, b / 2) * (b % 2 ? a : 1) % MOD : 1;
}
int C(int a, int b) {
    return 1LL * fact[b] * inv[a] % MOD * inv[b - a] % MOD;
}
void dfs(int v, int p) {
    c[v] = 1;
    par[v] = p;
    for (auto u : adj[v]) {
        if (u != p) {
            dfs(u, v);
            c[v] += c[u];
        }
    }
}
int F(int v) {
    return C(c[v], val[v] - f[v] + c[v]);
} 

void solve() {
    cin >> n >> r;
    for (int i = 0; i < n - 1; i++) {
        int v, u; cin >> v >> u;
        adj[v].pb(u), adj[u].pb(v);
    }
    int ans = C(n - 1, r + n - 1);
    val[1] = r;
    dfs(1, 0);
    c[1]--;
    cout << ans << '\n';

    int q; cin >> q;
    memset(val, -1, sizeof val);
    val[1] = r;
    while (q--) {
        int t, v; cin >> t >> v;
        if (t == 1) {
            int x; cin >> x;
            int u = par[v];
            while (val[u] == -1) {
                c[u] -= c[v];
                f[u] += x - f[v];
                u = par[u];
            }
            ans = 1LL * ans * binpow(F(u), MOD - 2) % MOD;
            c[u] -= c[v];
            f[u] += x - f[v];

            c[v]--;
            val[v] = x;

            ans = 1LL * ans * F(u) % MOD * F(v) % MOD;
        }
        else {
            int u = par[v]; 
            while (val[u] == -1) {
                c[u] += c[v] + 1;
                f[u] += f[v] - val[v];
                u = par[u];
            }
            ans = 1LL * ans * binpow(1LL * F(v) * F(u) % MOD, MOD - 2) % MOD;
            //cout << " ! " << F(v) << ' ' << F(u) << endl;
            f[u] += f[v] - val[v];
            c[u] += c[v] + 1;
            c[v]++;
            val[v] = -1;

            ans = 1LL * ans * F(u) % MOD;
            //cout << "? " << c[u] << ' '<< f[u] << endl;
        }
        cout << ans << '\n';
    }
}

int32_t main() {
    fact[0] = 1;
    for (int i = 1; i < N; i++)
        fact[i] = 1LL * i * fact[i - 1] % MOD;
    inv[N - 1] = binpow(fact[N - 1], MOD - 2);
    for (int i = N - 2; i >= 0; i--)
        inv[i] = 1LL * inv[i + 1] * (i + 1) % MOD;
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    solve();
    return 0;
}

• Subtask 1: 10 / 10
• Subtask 2: 20 / 20
• Subtask 3: 0 / 20
• Subtask 4: 0 / 20
• Subtask 5: 0 / 30