Submission #571717

#	Time	Username	Problem	Language	Result	Execution time	Memory
571717		BackNoob	Mousetrap (CEOI17_mousetrap)	C++14	100 / 100	864 ms	153420 KiB

mousetrap

#include <bits/stdc++.h>
#define ll long long
#define fi first
#define se second
#define endl '\n'
#define MASK(i) (1LL << (i))
#define ull unsigned long long
#define ld long double
#define pb push_back
#define all(x) (x).begin() , (x).end()
#define BIT(x , i) ((x >> (i)) & 1) 
#define TASK "task"
#define sz(s) (int) (s).size()

using namespace std;
const int mxN = 1e6 + 227;
const int inf = 1e9 + 277;
const int mod = 1e9 + 7;
const ll infll = 1e18 + 7;
const int base = 200;
const int LOG = 20;
 
template <typename T1, typename T2> bool minimize(T1 &a, T2 b) {
	if (a > b) {a = b; return true;} return false;
}
template <typename T1, typename T2> bool maximize(T1 &a, T2 b) {
	if (a < b) {a = b; return true;} return false;
}

int n;
int t;
int m;
int deg[mxN];
int dp[mxN];
int par[mxN];
bool spec[mxN];
vector<int> adj[mxN];
vector<int> path;

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

void calcdp(int u, int p)
{
	pair<int, int> best = {0, 0};
	for(int v : adj[u]) {
		if(v == p) continue;
		deg[u]++;
		calcdp(v, u);

		int tmp = best.fi;
		if(maximize(best.fi, dp[v]) == true) best.se = tmp;
		else maximize(best.se, dp[v]);
	}

	dp[u] = best.se + deg[u];
}

bool ok(int x)
{
	int sumdeg = 0;
	for(auto it : path) sumdeg += deg[it];

	if(sumdeg > x) return false;

	int cur = 0;
	int need = 0;
	for(auto u : path) {
		++cur;
		int re = 0;
		for(int v : adj[u]) {
			if(spec[v] == true) continue;
			re += (dp[v] + sumdeg) <= x;
			need += (dp[v] + sumdeg) > x;
		}
		sumdeg -= re;

		if(need > cur) return false;
	}
	return true;
}

void solve()
{	
	cin >> n >> t >> m;
	for(int i = 1; i < n; i++) {
		int u, v;
		cin >> u >> v;
		adj[u].pb(v);
		adj[v].pb(u);
	}

	par[m] = 0;
	dfs(m, -1);

	int pos = t;
	while(pos != 0) {
		if(pos != t) path.pb(pos);
		pos = par[pos];	
	}

	reverse(all(path));
	spec[t] = true;
	for(auto it : path) spec[it] = true;

	for(auto u : path) {
		for(int v : adj[u]) {
			if(spec[v] == false) {
				calcdp(v, u);
				deg[u]++;
			}
		}
	}

	// cout << dp[6] << ' ' << dp[7] << ' ' << dp[3] << endl;

	int lo = 0, hi = inf;
	while(lo + 1 < hi) {
		int mid = (lo + hi) / 2;
		if(ok(mid) == true) hi = mid;
		else lo = mid;
	}
	if(ok(lo)) cout << lo;
	else cout << hi;
}
 
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    //freopen(TASK".in" , "r" , stdin);
    //freopen(TASK".out" , "w" , stdout);
	

    int tc = 1;
    // cin >> tc;
    while(tc--) {
    	solve();
    }
    return 0;
}

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