Submission #563954

#	Time	Username	Problem	Language	Result	Execution time	Memory
563954		baokhue232005	Mousetrap (CEOI17_mousetrap)	C++17	100 / 100	764 ms	241332 KiB

mousetrap

/*
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimize("unroll-loops")
*/
// lethal option

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

#define all(flg) flg.begin(), flg.end()
#define pb push_back
#define fi first
#define se second
#define endl "\n"
#define eb emplace_back
#define ii pair<int, int>
#define PI 3.141592653589793238462643383279502884
#define ll long long
#define for1(i, ff, gg) for(int i = ff; i <= gg; ++i)
#define for2(i, ff, gg) for(int i = ff; i >= gg; --i)
const int mod = 998244353;
const int maxN = 2000005;
int n, a[maxN];
int x, y, z, k;
int s, t;

bool sacred[maxN];
int godlist[maxN];
int cn = 0;
vector<int> road[maxN];
int szi[maxN];
vector<int> burden[maxN];
vector<int> vc[maxN];

bool dfs_sacred(int node, int par){
    if(node == t){
        sacred[node] = 1; return 1;
    }
    for(int cc : vc[node]){
        if(dfs_sacred(cc, node)){
            sacred[node] = 1;
            godlist[++cn] = node; return 1;
        }
    }
    return 0;
}

int dfs_calc(int node, int par){
    for(int i = 0; i < (int)vc[node].size(); ++i){
        if(vc[node][i] == par){
            vc[node].erase(vc[node].begin() + i); break;
        }
    }
    for(int &cc : vc[node]) cc = dfs_calc(cc, node);
    sort(all(vc[node]), greater<int>());
    int res = 0;
    if(vc[node].size() >= 2) res = vc[node][1];
    return res + vc[node].size();
}

bool solve(int node, int lim, int turn){
    ++turn;
    if(node > n) return (lim >= 0);
    int fail = 0;
    for(int cc : road[node]) if(cc + szi[node] > lim) ++fail;
    if(turn < fail) return 0;
    turn -= fail; lim -= fail;
    return solve(node + 1, lim, turn);
}

signed main(){
    // freopen("mousetrap.inp", "r", stdin);
    // freopen("mousetrap.out", "w", stdout);

    ios_base::sync_with_stdio(0);
    cin.tie(NULL);
    cout.tie(NULL);
    cin >> n >> t >> s;
    if(s == t){
        cout << 0 << endl; exit(0);
    }
    memset(sacred, 0, sizeof(sacred));
    for1(i, 2, n){
        cin >> x >> y;
        vc[x].pb(y);
        vc[y].pb(x);
    }
    // if(n > 10) exit(0);
    dfs_sacred(s, s);
    reverse(godlist + 1, godlist + cn + 1);
    z = 0;
    vector<ii> dawut;
    for1(i, 1, n) if(!sacred[i]){
        int saved = 0;
        for(int cc : vc[i]) if(sacred[cc] && cc != t)
            dawut.pb({i, cc});
    }
    for(ii pr : dawut){
        burden[pr.se].pb(dfs_calc(pr.fi, pr.se));
    }
    // if(n > 10) exit(0);
    n = cn;
    for1(i, 1, n){
        swap(road[i], burden[godlist[i]]);
        szi[i] = road[i].size();
        // cout << szi[i] << endl;
        // for(int cc : road[i]) cout << cc << " ";
        // cout << endl;
    }
    z = 0;
    for2(i, n, 1){
        z += szi[i]; szi[i] = z;
    }
    int le = 0, ri = 1e7;
    while(le != ri){
        int mid = (le + ri) / 2;
        if(solve(1, mid, 0)) ri = mid;
        else le = mid + 1;
    }
    cout << le << endl;
}

Compilation message (stderr)

mousetrap.cpp: In function 'int main()':
mousetrap.cpp:95:13: warning: unused variable 'saved' [-Wunused-variable]
   95 |         int saved = 0;
      |             ^~~~~

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