Submission #564087

#	Time	Username	Problem	Language	Result	Execution time	Memory
564087		hollwo_pelw	Mousetrap (CEOI17_mousetrap)	C++17	100 / 100	795 ms	153900 KiB

mousetrap

#include <bits/stdc++.h>
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/trie_policy.hpp>
// #include <ext/rope>

using namespace std;
// using namespace __gnu_cxx;
// using namespace __gnu_pbds;

void Hollwo_Pelw();

signed main(){
#ifndef hollwo_pelw_local
	if (fopen("mousetrap.inp", "r"))
		assert(freopen("mousetrap.inp", "r", stdin)), assert(freopen("mousetrap.out", "w", stdout));
#else
	auto start = chrono::steady_clock::now();
#endif
	cin.tie(0), cout.tie(0) -> sync_with_stdio(0);
	int testcases = 1;
	// cin >> testcases;
	for (int test = 1; test <= testcases; test++){
		// cout << "Case #" << test << ": ";
		Hollwo_Pelw();
	}
#ifdef hollwo_pelw_local
	auto end = chrono::steady_clock::now();
	cout << "\nExcution time : " << chrono::duration_cast<chrono::milliseconds> (end - start).count() << "[ms]" << endl;
#endif
}

const int N = 1e6 + 5;

int n, s, t, deg[N], dp[N], par[N], in_path[N];
vector<int> adj[N];

void find_path(int u, int p) {
    par[u] = p;
    for (int v : adj[u])
        if (v != p) find_path(v, u);
}

void calc_dp(int u, int p) {
    int m1 = 0, m2 = 0;
    for (int v : adj[u]) if (v != p) {
        deg[u] ++;
        calc_dp(v, u);
        int f = dp[v];
        if (f > m1) swap(f, m1);
        if (f > m2) swap(f, m2);
    }
    dp[u] = deg[u] + m2;
}

bool check(int mid) {
    int tot = 0;
    for (int u = s; par[u]; u = par[u])
        tot += deg[u];

    if (tot > mid) return 0;

    for (int u = s, cnt = 0, cur = 1; par[u]; u = par[u], cur ++) {
        int ign = 0;
        for (int v : adj[u]) if (!in_path[v]) {
            ign += tot + dp[v] <= mid;
            cnt += tot + dp[v] >  mid;
        }
        tot -= ign;
        if (cnt > cur) return 0;
    }

    return 1;
}

void Hollwo_Pelw(){
    cin >> n >> t >> s;
    for (int i = 1, u, v; i < n; i++) {
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    find_path(t, 0);

    for (int u = s; u; u = par[u])
        in_path[u] = 1;

    for (int u = s; par[u]; u = par[u]) {
        for (int v : adj[u]) if (!in_path[v]) {
            deg[u] ++;
            calc_dp(v, u);
        }
    }

    int l = 0, r = 2 * n;
    while (l < r) {
        int m = (l + r) >> 1;
        if (check(m))
            r = m;
        else
            l = m + 1;
    }
    cout << l;
}

• Subtask 1: 20 / 20
• Subtask 2: 25 / 25
• Subtask 3: 20 / 20
• Subtask 4: 35 / 35