Submission #1197872

#	Time	Username	Problem	Language	Result	Execution time	Memory
1197872		Zbyszek99	Mousetrap (CEOI17_mousetrap)	C++20	25 / 100	837 ms	71996 KiB

mousetrap

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ll long long
#define ld long double
#define ull unsigned long long
#define ff first
#define ss second
#define pii pair<int,int>
#define pll pair<long long, long long>
#define vi vector<int>
#define vl vector<long long>
#define pb push_back
#define rep(i, b) for(int i = 0; i < (b); ++i)
#define rep2(i,a,b) for(int i = a; i <= (b); ++i)
#define rep3(i,a,b,c) for(int i = a; i <= (b); i+=c)
#define count_bits(x) __builtin_popcountll((x))
#define all(x) (x).begin(),(x).end()
#define siz(x) (int)(x).size()
#define forall(it,x) for(auto& it:(x))
using namespace __gnu_pbds;
using namespace std;
typedef tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;
//mt19937 mt;void random_start(){mt.seed(chrono::time_point_cast<chrono::milliseconds>(chrono::high_resolution_clock::now()).time_since_epoch().count());}
//ll los(ll a, ll b) {return a + (mt() % (b-a+1));}
const int INF = 1e9+50;
const ll INF_L = 1e18+40;
const ll MOD = 1e9+7;

vi graph[1000001];
int tdist[1000001];
int ans[1000001];
int dp[1000001];
int P[1000001];
bool path[1000001];
vi p;
int n,t,m;

void dfs_tdist(int v, int pop, int d, int cur_ans = 0)
{
    P[v] = pop;
    tdist[v] = d++;
    cur_ans += siz(graph[v])-2;
    if(siz(graph[v]) == 1) cur_ans++;
    if(v == pop)  cur_ans = 0;
    ans[v] = cur_ans;
    forall(it,graph[v])
    {
        if(it != pop) 
        {
            dfs_tdist(it,v,d,cur_ans);
        }
    }
}

void dfs_mdist(int v, int pop, int min_dep)
{
    min_dep = min(min_dep,tdist[v]);
    ans[v] += tdist[v] - min_dep;
    forall(it,graph[v])
    {
        if(it != pop)
        {
            dfs_mdist(it,v,min_dep);
        }
    }
}

void dfs_dp(int v, int pop)
{
    vi dps;
    forall(it,graph[v])
    {
        if(it != pop)
        {
            dfs_dp(it,v);
            dps.pb(dp[it]);
        }
    }
    sort(all(dps));
    reverse(all(dps));
    if(siz(dps) >= 2) dp[v] = dps[1];
    else if(siz(dps) == 1) dp[v] = min(ans[v]+1,dps[0]);
    else dp[v] = ans[v];
}

bool check(int ans)
{
    int cur_moves = 1;
    int cur_used = 0;
    forall(v,p)
    {
        int prev_used = cur_used;
        forall(it,graph[v])
        {
            if(path[it]) continue;
            if(prev_used + dp[it] > ans)
            {
                cur_moves--;
                cur_used++;
            }
        }
        if(cur_moves < 0) return 0;
        cur_moves++;
    }
    if(cur_used <= ans)
    {
        return 1;
    }
    return 0;
}

int main()
{
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    //random_start();
    cin >> n >> t >> m;
    rep(i,n-1)
    {
        int a,b;
        cin >> a >> b;
        graph[a].pb(b);
        graph[b].pb(a);
    }
    dfs_tdist(t,t,0);
    dfs_mdist(m,m,tdist[m]);
    int cur = m;
    while(cur != t)
    {
        path[cur] = 1;
        p.pb(cur);
        cur = P[cur];
    }
    path[t] = 1;
    forall(it,p)
    {
        forall(it2,graph[it])
        {
            if(path[it2]) continue;
            dfs_dp(it2,it);
        }
    }
    int l = 0;
    int r = n*2;
    int ans = -1;
    while(l <= r)
    {
        int mid = (l+r)/2;
        if(check(mid))
        {
            ans = mid;
            r = mid-1;
        }
        else
        {
            l = mid+1;
        }
    }
    cout << ans << "\n";
}

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