Submission #47059

#	Time	Username	Problem	Language	Result	Execution time	Memory
47059		RockyB	Mousetrap (CEOI17_mousetrap)	C++17	25 / 100	1022 ms	60388 KiB

mousetrap

/// In The Name Of God
 
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
 
#include <bits/stdc++.h>
 
#define f first
#define s second
 
#define pb push_back
#define pp pop_back
#define mp make_pair
 
#define sz(x) (int)x.size()
#define sqr(x) ((x) * 1ll * (x))
#define all(x) x.begin(), x.end()
 
#define Kazakhstan ios_base :: sync_with_stdio(0), cin.tie(0), cout.tie(0);
 
#define nl '\n'
#define ioi exit(0);
 
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
 
const int N = (int)1e6 + 7;
const int inf = (int)1e9 + 7;
const int mod = (int)1e9 + 7;
const ll linf = (ll)1e18 + 7;
 
const int dx[] = {-1, 0, 1, 0, 1, -1, -1, 1};
const int dy[] = {0, 1, 0, -1, 1, -1, 1, -1};
 
using namespace std;
 
int n, t, m;
int dp[N], jump[N];
bool ok[N];

vector <int> g[N];
 
void dfs0(int v = m, int p = -1) {
	if (v == t) ok[v] = 1;
	for (auto to : g[v]) {
		if (to == p) continue;
		dfs0(to, v);
		if (ok[to]) {
			ok[v] = 1;
			jump[v] = to;
		}
	}
}
int dfs(int v = m, int p = t) {
	if (~dp[v]) return dp[v];

	{
		int cnt = 0;
		for (auto to : g[v]) {
			if (to == p) continue;
			++cnt;
		}
		if (cnt <= 1) return dp[v] = cnt;
	}
	
	int id1 = -1, id2 = -1, sz = 0;
	for (int i = 0; i < sz(g[v]); i++) {
		int to = g[v][i];
		if (to == p) continue;
		if (id1 == -1 || dfs(to, v) > dfs(id1, v)) id1 = to;
		++sz;	
	}
	for (int i = 0; i < sz(g[v]); i++) {
		int to = g[v][i];
		if (to == p || to == id1) continue;
		if (id2 == -1 || dfs(to, v) > dfs(id2, v)) id2 = to;
	}
	return dp[v] = dfs(id2, v) + sz;
}

bool dbg;
int solve(int v = m, int p = -1) {
	if (v == t) {
		return 0;
		if (p == -1) return 0;
		return -1;
	}
	if (!ok[v]) return dfs(v, p);

	int id1 = -1, id2 = -1, sz = 0;
	for (int i = 0; i < sz(g[v]); i++) {
		int to = g[v][i];
		if (to == p || ok[to]) continue;
		if (id1 == -1 || dfs(to, v) > dfs(id1, v)) id1 = to;
		++sz;	
	}
	for (int i = 0; i < sz(g[v]); i++) {
		int to = g[v][i];
		if (to == p || to == id1 || ok[to]) continue;
		if (id2 == -1 || dfs(to, v) > dfs(id2, v)) id2 = to;
	}
	if (id2 == -1) return solve(jump[v], v) + 1;
	return solve(jump[v], v) + dfs(id2, v) + sz;
}
int main() {
	#ifdef IOI2018
		freopen ("in.txt", "r", stdin);
	#endif
	Kazakhstan
	cin >> n >> t >> m;
	for (int i = 1; i < n; i++) {
		int v, u;
		cin >> v >> u;
		g[v].pb(u);
		g[u].pb(v);
	}
	dfs0();
	memset(dp, -1, sizeof(dp));
	cout << solve();
	ioi
}

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