Submission #161608

#	Time	Username	Problem	Language	Result	Execution time	Memory
161608		shayan_p	Mousetrap (CEOI17_mousetrap)	C++14	100 / 100	1123 ms	198952 KiB

mousetrap

// Remember...

#include<bits/stdc++.h>

#define F first
#define S second
#define PB push_back
#define sz(s) int((s).size())
#define bit(n,k) (((n)>>(k))&1)

using namespace std;

typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

const int maxn=1e6+10,mod=1e9+7;
const ll inf=1e18;

vector<int> v[maxn], dps[maxn], path;
int dp[maxn], pr[maxn];

bool mark[maxn];

void dfs(int u,int par){
    pr[u]=par;
    int id=-1, cnt=0;
    for(int y:v[u]){
	if(y!=par){
	    cnt++;
	    dfs(y,u);
	    if(id==-1 || dp[id]<dp[y])
		id=y;
	}
    }
    for(int y:v[u]){
	if(y!=par && y!=id)
	    dp[u]=max(dp[u], dp[y]);
    }
    dp[u]+=cnt;
}

bool ok(int lm){
    int tot=0, usd=0;
    for(int i=0;i<sz(path);i++){
	tot+=sz(dps[i]);
    }
    for(int i=0;i<sz(path);i++){
	usd++;
	int pt=0, cnt=0;
	while(pt<sz(dps[i]) && dps[i][pt]+tot>lm)
	    usd--, pt++, cnt++;
	lm-=cnt;
	tot-=sz(dps[i]);
	if(usd<0 || lm<0) return 0;
    }
    return 1;
}

int main(){
    ios_base::sync_with_stdio(false); cin.tie(0); cout.tie();

    int n,t,m; cin>>n>>t>>m;
    for(int i=0;i<n-1;i++){
	int a,b; cin>>a>>b;
	v[a].PB(b);
	v[b].PB(a);
    }
    dfs(t,-1);
    
    int tmp=m;
    while(tmp!=t){
	mark[tmp]=1;
	path.PB(tmp);
	tmp=pr[tmp];
    }
    mark[t]=1;

    for(int i=0;i<sz(path);i++){
	for(int u:v[path[i]]){
	    if(mark[u]==0)
		dps[i].PB(dp[u]);
	}
	sort(dps[i].begin(),dps[i].end(),greater<int>());
    }
    int l=-1,r=n-1;
    while(r-l>1){
	int mid=(l+r)>>1;
	if(ok(mid)) r=mid;
	else l=mid;
    }    
    return cout<<r<<endl,0;
}
// Deathly mistakes:
//  * Read the problem carefully.
//  * Check maxn.
//  * Overflows.


// #pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

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