Submission #819753

#	Time	Username	Problem	Language	Result	Execution time	Memory
819753		stefanopulos	Torrent (COI16_torrent)	C++17	100 / 100	94 ms	33708 KiB

torrent

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <bits/stdc++.h>
 
using namespace std;
using namespace __gnu_pbds;
 
typedef long long ll;
typedef long double ldb;
 
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef pair<ldb,ldb> pdd;

#define ff(i,a,b) for(int i = a; i <= b; i++)
#define fb(i,b,a) for(int i = b; i >= a; i--)
#define trav(a,x) for(auto& a : x)
 
#define sz(a) (int)(a).size()
#define fi first
#define se second
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
 
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

// os.order_of_key(k) the number of elements in the os less than k
// *os.find_by_order(k)  print the k-th smallest number in os(0-based)

const int mod = 1000000007;
const int inf = 1e9 + 5;
const int mxN = 300005; 

int n, a, b;

vector<int> g[mxN];

int par[mxN];
void dfs1(int v, int p){
    par[v] = p;
    for(auto u : g[v]){
        if(u != p)dfs1(u, v);
    }
}

bool bio[mxN];
int dfs2(int v, int p){

    vector<int> vec;
    for(auto u : g[v]){
        if(u != p){
            int X = dfs2(u, v);
            vec.pb(X);
        }
    }

    int kol = 0; sort(rall(vec));
    ff(i,0,sz(vec) - 1)kol = max(kol, i + 1 + vec[i]);

    return kol;

}

int m = 0;
vector<int> kol[mxN];

bool pref[mxN];
bool sufi[mxN];
bool check(int X){
    ff(i,1,m)pref[i] = sufi[i] = 0;

    int uk = 0; pref[0] = 1;
    ff(i,1,m){


        int len = sz(kol[i]); int ide = len + 1, mn = 0;
        ff(j,1,len){
            int z = X - kol[i][j - 1] - uk;

            while(z < ide){
                mn = ide;
                ide -= 1;
            }

            ide -= 1;

        }

        if(ide > 0)mn = 1;

        if(ide < 0){
            // los
            break;
        }


        pref[i] = 1; uk += mn;
    }

    uk = 0; sufi[m + 1] = 1;
    fb(i,m,1){

        int len = sz(kol[i]); int ide = len + 1, mn = 0;
        ff(j,1,len){
            int z = X - kol[i][j - 1] - uk;

            while(z < ide){
                mn = ide;
                ide -= 1;
            }

            ide -= 1;

        }

        if(ide > 0)mn = 1;

        if(ide < 0){
            // los
            break;
        }


        sufi[i] = 1; uk += mn;
    }

    ff(i,0,m)if(pref[i] && sufi[i + 1])return 1;
    return 0;

}

int main(){
    cin.tie(0)->sync_with_stdio(0);

    cin >> n >> a >> b;
    ff(i,1,n - 1){
        int u, v;
        cin >> u >> v;
        g[u].pb(v);
        g[v].pb(u);
    }

    dfs1(a, -1);

    vector<int> put;
    for(int i = b; i != -1; i = par[i]){
        put.pb(i); bio[i] = 1;
    }

    m = sz(put);
    ff(i,0,m - 1){
        for(auto f : g[put[i]]){
            if(!bio[f]){
                int X = dfs2(f, put[i]);
                kol[i + 1].pb(X);
            }
        }
        sort(all(kol[i + 1]));
    }    

    int l = 1, r = n, ans = 0;
    while(l <= r){
        int mid = (l + r) / 2;
        if(check(mid)){
            ans = mid;
            r = mid - 1;
        }
        else l = mid + 1;
    }

    cout << ans << '\n';

    return 0;
}
/*



// probati bojenje sahovski
*/
 
 
 
 
 

• Subtask 1: 31 / 31
• Subtask 2: 69 / 69