Submission #950570

#	Time	Username	Problem	Language	Result	Execution time	Memory
950570		GrindMachine	Mousetrap (CEOI17_mousetrap)	C++17	25 / 100	891 ms	60240 KiB

mousetrap

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
 
using namespace std;
using namespace __gnu_pbds;
 
template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
 
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) (int)a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x,y) ((x+y-1)/(y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl
 
#define rep(i,n) for(int i = 0; i < n; ++i)
#define rep1(i,n) for(int i = 1; i <= n; ++i)
#define rev(i,s,e) for(int i = s; i >= e; --i)
#define trav(i,a) for(auto &i : a)
 
template<typename T>
void amin(T &a, T b) {
    a = min(a,b);
}
 
template<typename T>
void amax(T &a, T b) {
    a = max(a,b);
}
 
#ifdef LOCAL
#include "debug.h"
#else
#define debug(x) 42
#endif
 
/*
 
refs:
https://youtu.be/OH1U-ujZTuc?list=PLg_Krngrs0eC_1vn0dTjyPZMkwBOcVsgH
edi
 
*/
 
const int MOD = 1e9 + 7;
const int N = 1e6 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;
 
vector<int> adj[N];
vector<int> curr_path, path;

void dfs1(int u, int p, int des){
    curr_path.pb(u);
    if(u == des){
        path = curr_path;
    }

    trav(v,adj[u]){
        if(v == p) conts;
        dfs1(v,u,des);
    }

    curr_path.pop_back();
}

vector<int> dp(N);
vector<bool> on_path(N);

void dfs2(int u, int p){
    vector<int> vals;

    trav(v,adj[u]){
        if(v == p or on_path[v]) conts;
        dfs2(v,u);
        vals.pb(dp[v]);
    }
    
    dp[u] = sz(vals);

    vals.pb(0), vals.pb(0); 
    sort(rall(vals));
    dp[u] += vals[1];
}
 
void solve(int test_case)
{
    int n,t,m; cin >> n >> t >> m;
    rep1(i,n-1){
        int u,v; cin >> u >> v;
        adj[u].pb(v), adj[v].pb(u);
    }

    dfs1(m,-1,t);

    trav(u,path) on_path[u] = 1;
    path.pop_back();

    vector<pii> branches;

    rep(i,sz(path)){
        int u = path[i];
        trav(v,adj[u]){
            if(on_path[v]) conts;
            dfs2(v,-1);
            branches.pb({i+1,dp[v]});
        }
    }

    rep(i,sz(branches)){
        branches[i].ss += sz(branches)-i;
    }

    auto ok = [&](int mid){
        int b = 0;
        for(auto [d,val] : branches){
            if(b+val > mid){
                if(b >= d){
                    return false;
                }

                b++;
            }
        }

        return b <= mid;
    };

    int l = 0, r = 2*n;
    int ans = -1;

    while(l <= r){
        int mid = (l+r) >> 1;
        if(ok(mid)){
            ans = mid;
            r = mid-1;
        }
        else{
            l = mid+1;
        }
    }

    cout << ans << endl;
}
 
int main()
{
    fastio;
 
    int t = 1;
    // cin >> t;
 
    rep1(i, t) {
        solve(i);
    }
 
    return 0;
}

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