Submission #266839

#	Time	Username	Problem	Language	Result	Execution time	Memory
266839		MarcoMeijer	Mousetrap (CEOI17_mousetrap)	C++14	25 / 100	961 ms	107768 KiB

mousetrap

#include <bits/stdc++.h>
using namespace std;

// macros
typedef long long ll;
typedef long double ld;
typedef pair<int, int> ii;
typedef pair<ll, ll> lll;
typedef tuple<int, int, int> iii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<iii> viii;
typedef vector<ll> vll;
typedef vector<lll> vlll;
#define REP(a,b,c) for(int a=int(b); a<int(c); a++)
#define RE(a,c) REP(a,0,c)
#define RE1(a,c) REP(a,1,c+1)
#define REI(a,b,c) REP(a,b,c+1)
#define REV(a,b,c) for(int a=int(c-1); a>=int(b); a--)
#define FOR(a,b) for(auto& a : b)
#define all(a) a.begin(), a.end()
#define INF 1e9
#define EPS 1e-9
#define pb push_back
#define popb pop_back
#define fi first
#define se second
#define sz size()
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());

// input
template<class T> void IN(T& x) {cin >> x;}
template<class H, class... T> void IN(H& h, T&... t) {IN(h); IN(t...); }

// output
template<class T1, class T2> void OUT(const pair<T1,T2>& x);
template<class T> void OUT(const T& x) {cout << x;}
template<class H, class... T> void OUT(const H& h, const T&... t) {OUT(h); OUT(t...); }
template<class T1, class T2> void OUT(const pair<T1,T2>& x) {OUT(x.fi,' ',x.se);}
template<class... T> void OUTL(const T&... t) {OUT(t..., "\n"); }
template<class H> void OUTLS(const H& h) {OUTL(h); }
template<class H, class... T> void OUTLS(const H& h, const T&... t) {OUT(h,' '); OUTLS(t...); }

//===================//
//  Added libraries  //
//===================//

//===================//
//end added libraries//
//===================//

void program();
int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    program();
}


//===================//
//   begin program   //
//===================//

const int MX = 1e6+10;

int n, t, m;
int a[MX], b[MX];
int sm[MX];
vi adj[MX];
vi path;

bool dfsPath(int u, int p=-1) {
    if(u == 1) {
        path.pb(u);
        return 1;
    }
    FOR(v,adj[u]) if(v != p) {
        if(dfsPath(v,u)) {
            path.pb(u);
            return 1;
        }
    }
    return 0;
}

int dp[MX];
vi res[MX];
void dfsDP(int u, int p=-1) {
    FOR(v,adj[u]) if(v != p) dfsDP(v,u);

    FOR(v,adj[u]) if(v != p) {
        res[u].pb(dp[v]);
    }
    sort(all(res[u]), greater<int>());
    if(res[u].sz <= 1) dp[u] = res[u].sz;
    else dp[u] = res[u][1]+res[u].sz;
}
void createDP(int u, int p=-1, int op=-1) {
    FOR(v,adj[u]) if(v != p && v != op) {
        dfsDP(v,u);
        res[u].pb(dp[v]);
    }
    sort(all(res[u]), greater<int>());
}

bool possible(int ub) {
    int canRem=1, rem=0;
    RE(i,path.sz-1) {
        int mx = ub - sm[i] - rem;
        int u = path[i];
        RE(j,res[u].sz) {
            if(res[u][j] > mx) {
                rem++;
                canRem--;
            }
        }
        if(canRem < 0) return 0;
        canRem++;
    }
    return 1;
}

void program() {
    IN(n,t,m);
    RE(i,n-1) IN(a[i], b[i]);
    RE(i,n) adj[a[i]].pb(b[i]);
    RE(i,n) adj[b[i]].pb(a[i]);

    if(t == m) {
        OUTL(0);
        return;
    }

    dfsPath(m);
    reverse(all(path));

    sm[path.sz-1] = 0;
    REV(i,0,path.sz-1) {
        sm[i] = sm[i+1] + adj[path[i]].sz-2;
    }
    sm[0]++;
    RE(i,path.sz-1) {
        if(i == 0) createDP(path[i],path[i+1]);
        else createDP(path[i],path[i+1],path[i-1]);
    }

    int lb=0, ub=INF;
    while(lb != ub) {
        int mid=(lb+ub)/2;
        if(possible(mid)) ub=mid;
        else lb=mid+1;
    }

    if(sm[1] == 0 && adj[m].sz == 1) lb = 0;

    OUTL(lb);
}

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