Submission #419020

#	Time	Username	Problem	Language	Result	Execution time	Memory
419020		egekabas	Mousetrap (CEOI17_mousetrap)	C++14	45 / 100	3333 ms	90104 KiB

mousetrap

#include <bits/stdc++.h>
#define all(x) (x).begin(), (x).end()
#define ff first
#define ss second
#define pb push_back
#define mp make_pair
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pull;
typedef pair<ll, ll> pii;
typedef pair<ld, ld> pld;
ll n, t, m;
vector<ll> g[1000009];
ll trap[1000009];
ll dp[1000009];
ll edgecnt[1000009];

void dfs(ll v, ll prt){
    if(v == t){
        trap[v] = 1;
        return;
    }
    for(auto u : g[v])
        if(u != prt){
            dfs(u, v);
            if(trap[u])
                trap[v] = 1;
            else
                ++edgecnt[v];
        }
    dp[v] = edgecnt[v];
    for(auto u : g[v])
        if(u != prt && trap[u])
            dp[v] += dp[u];
}
ll getans(ll v, ll prt, ll curval){
    if(v == t) return 0;
    if(trap[v] == 0)
        curval -= edgecnt[v];
    if(curval < 0){
        //cout << v << ' ' << 1e9 << '\n';
        return 1e9;
    }
    ll sum = 0;
    for(auto u : g[v])
        if(u != prt){
            if(trap[u] == 0)
                sum += min(1LL, getans(u, v, curval));
            else
                sum += getans(u, v, curval);
        }
            
    //cout << v << ' ' << min((ll)1e9, max(sum-1, 0LL)) << '\n';
    return min((ll)1e9, max(sum-1, 0LL));
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    
    //freopen("in.txt", "r", stdin);
    //freopen("out.txt", "w", stdout);

    cin >> n >> t >> m;
    for(ll i = 0; i < n-1; ++i){
        ll x, y;
        cin >> x >> y;
        g[x].pb(y);
        g[y].pb(x);
    }
    dfs(m, 0);
    ll l = 0, r = n;
    while(l < r){
        ll mid = (l+r)/2;
        if(getans(m, 0, mid-dp[m]) == 0)
            r = mid;
        else
            l = mid+1;
    }
    cout << l << '\n';
}

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