Submission #374994

#	Time	Username	Problem	Language	Result	Execution time	Memory
374994		YJU	Mousetrap (CEOI17_mousetrap)	C++14	25 / 100	813 ms	78572 KiB

mousetrap

#include<bits/stdc++.h>
#pragma GCC optimize("unroll-loops,no-stack-protector,Ofast")
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> pll;
const ll MOD=1e9+7;
const ll MOD2=998244353;
const ll N=1e6+5;
const ld pi=acos(-1);
const ll INF=(1LL<<30);
#define SQ(i) ((i)*(i))
#define REP(i,n) for(ll i=0;i<n;i++)
#define REP1(i,n) for(ll i=1;i<=n;i++)
#define pb push_back
#define mp make_pair
#define X first
#define Y second
#define setp setprecision
#define lwb lower_bound
#define SZ(_a) (ll)_a.size()

ll n,t,s,dp[N],x,y,fa[N],dg[N];
vector<ll> v[N];

void DFS(ll nd,ll pa){
	
	fa[nd]=pa;
	
	ll ma=0,mb=0;
	for(auto i:v[nd]){
		if(i==pa)continue;
		DFS(i,nd);
		if(dp[i]>=ma)mb=ma,ma=dp[i];
		else if(dp[i]>=mb)mb=dp[i];
	}
	dp[nd]=mb+SZ(v[nd])-1;
}

ll lis[N],now;

bool ck(ll k){
	ll ti=0;
	for(int i=1;i<now;i++){
		ll tmp=0;
		for(auto j:v[lis[i]]){
			if(j==lis[i+1]||j==lis[i-1])continue;
			if(dg[i]+dp[j]+1-(i!=1)>k)++tmp;
		}
		ti+=tmp;k-=tmp;
		if(k<0||ti>i)return 0;
	}
	return 1;
}

int main(){
	ios_base::sync_with_stdio(0);cin.tie(0);
	cin>>n>>t>>s;
	REP(i,n-1)cin>>x>>y,v[x].pb(y),v[y].pb(x);
	
	if(s==t){cout<<"0\n";return 0;}
	
	DFS(t,0);
	
	dp[t]=0;
	
	for(int i=s;i;i=fa[i])lis[++now]=i;
	for(int i=now-1;i>=0;i--)dg[i]=dg[i+1]+SZ(v[lis[i]])-1-(lis[i]!=t);
	
	ll r=INF,l=0;
	while(l<r-1){
		ll mid=(r+l)>>1;
		(ck(mid)?r=mid:l=mid);
	}
	cout<<r<<"\n";
	return 0;
}

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