Submission #45098

#	Time	Username	Problem	Language	Result	Execution time	Memory
45098		qoo2p5	Mousetrap (CEOI17_mousetrap)	C++17	25 / 100	1315 ms	61564 KiB

mousetrap

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;

const int INF = (int) 1e9 + 1e6 + 123;
const ll LINF = (ll) 1e18 + 1e9 + 123;

#define rep(i, s, t) for (auto i = (s); i < (t); ++(i))
#define per(i, s, t) for (auto i = (s); i >= (t); --(i))
#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define mp make_pair
#define pb push_back

bool mini(auto &x, const auto &y) {
	if (y < x) {
		x = y;
		return 1;
	}
	return 0;
}

bool maxi(auto &x, const auto &y) {
	if (y > x) {
		x = y;
		return 1;
	}
	return 0;
}

void run();

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	run();
	return 0;
}

const int N = (int) 1e6 + 123;

int n, t, m;
vector<int> g[N];
int dp[N], out[N];
bool has[N];

void dfs(int v, int f = -1) {
	if (v == t) {
		has[v] = 1;
		return;
	}
	
	int pos = -1;
	int ptr = 0;
	for (int u : g[v]) {
		if (u == f) {
			pos = ptr;
			ptr++;
			continue;
		}
		dfs(u, v);
		has[v] |= has[u];
		ptr++;
	}
	if (pos != -1) {
		g[v].erase(g[v].begin() + pos);
	}
	
	vector<int> outs;
	for (int u : g[v]) {
		outs.pb(out[u]);
	}
	if (sz(outs) == 0) {
		out[v] = 0;
	} else if (sz(outs) == 1) {
		out[v] = 1;
	} else {
		sort(all(outs));
		int k = sz(outs);
		out[v] = outs[k - 2] + k;
	}
}

int solve(int v, bool flag) {
	if (v == t) {
		return 0;
	}
	
	assert(has[v]);
	int to = -1;
	for (int u : g[v]) {
		if (has[u]) {
			to = u;
		}
	}
	assert(to != -1);
	
	int cur;
	
	if (flag) {
		cur = sz(g[v]) - 1;
	} else {
		vector<int> outs;
		for (int u : g[v]) {
			if (u == to) {
				continue;
			}
			outs.pb(out[u]);
		}
		sort(all(outs));
		if (sz(outs) == 0) {
			cur = 0;
		} else if (sz(outs) == 1) {
			cur = 1;
			flag = 1;
		} else {
			int k = sz(outs);
			cur = outs[k - 2] + k;
			flag = 1;
		}
	}
	
	return cur + solve(to, flag);
}

void run() {
	cin >> n >> t >> m;
	rep(i, 0, n - 1) {
		int u, v;
		cin >> u >> v;
		g[u].pb(v);
		g[v].pb(u);
	}
	
	dfs(m);
	cout << solve(m, false) << "\n";
}

• Subtask 1: 0 / 20
• Subtask 2: 25 / 25
• Subtask 3: 0 / 20
• Subtask 4: 0 / 35