Submission #973313

#	Time	Username	Problem	Language	Result	Execution time	Memory
973313		efedmrlr	Mousetrap (CEOI17_mousetrap)	C++17	25 / 100	628 ms	91256 KiB

mousetrap

// #pragma GCC optimize("O3,Ofast,unroll-loops")
// #pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#include <bits/stdc++.h>

using namespace std;


#define lli long long int
#define MP make_pair
#define pb push_back
#define REP(i,n) for(int i = 0; (i) < (n); (i)++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()


void fastio() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
}


const double EPS = 0.00001;
const int INF = 1e9+500;
const int N = 1e6 + 5;
const int ALPH = 26;
const int LGN = 25;
constexpr int MOD = 1e9+7;
int n,t,m;

vector<int> dp(N, 0);
vector<vector<int> > adj(N, vector<int>());
vector<vector<int> > vs(N, vector<int>());
vector<int > suf;
int mxd = 0;
void dfs(int node, int par) {
    for(auto c : adj[node]) {
        if(c == par) continue;
        dfs(c, node);
    }
    array<int, 2> mx = {0, 0};
    for(auto c : adj[node]) {
        if(c == par) continue;
        if(dp[c] > mx[0]) {
            swap(mx[0], mx[1]);
            mx[0] = dp[c];
        }
        else if(dp[c] > mx[1]) {
            mx[1] = dp[c];
        }
    }
    dp[node] = mx[1] + (int)adj[node].size() - 1; 

}

int dfs2(int node, int par, int dist = 0) {
    if(node == t) {
        mxd = dist;
        return node;
    }
    int ret = 0;
    for(auto c : adj[node]) {
        if(c == par) continue;
        ret = dfs2(c, node, dist + 1);
        if(ret) {
            break;
        }
    }
    if(!ret) return 0;
    for(auto c : adj[node]) {
        if(c == par || c == ret) continue;
        dfs(c, node);
        vs[dist].pb(dp[c]);
        // cout << "c:" << c << " dp:" << dp[c] << " dist:" << dist << "\n";
    }
    return node;
}

bool check(int tar) {
    int stam = 1;
    for(int i = 0; i < mxd; i++) {
        for(auto c : vs[i]) {
            if(c + suf[i] > tar) {
                if(!stam) return 0;
                stam--;
            }
        }
        stam++;
    }
    return 1;
}

inline void solve() {
    cin>>n>>t>>m;
    REP(i, n - 1) {
        int u, v;
        cin >> u >> v;
        adj[u].pb(v);
        adj[v].pb(u);
    }
    dfs2(m, 0);
    for(int i = 0; i < mxd; i++) {
        sort(rall(vs[i]));
    }
    suf.assign(mxd + 3, 0);
    for(int i = mxd - 1; i>=0; i--) {
        suf[i] = suf[i + 1] + (int)vs[i].size();
    }
    int tl = 0, tr = n;
    while(tl < tr) {
        int tm = (tl + tr) >> 1;
        if(check(tm)) {
            tr = tm;
        }
        else {
            tl = tm + 1;
        }
    } 
    if(!check(tl)) tl++;
    cout << tl << "\n"; 
    
}
 
signed main() {

    fastio();
    int test = 1;
    //cin>>test;
    while(test--) {
        solve();
    }
    
}

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