Submission #1087239

#	Time	Username	Problem	Language	Result	Execution time	Memory
1087239		TrinhKhanhDung	Torrent (COI16_torrent)	C++14	100 / 100	240 ms	27244 KiB

torrent

#include <bits/stdc++.h>
#define ll long long
#define fi first
#define se second
#define sz(x) (int)x.size()
#define ALL(v) v.begin(),v.end()
#define MASK(k) (1LL << (k))
#define BIT(x, i) (((x) >> (i)) & 1)
#define oo (ll)1e18
#define INF (ll)1e9
#define MOD (ll)(1e9 + 7)

using namespace std;

template<class T1, class T2>
    bool maximize(T1 &a, T2 b){if(a < b){a = b; return true;} return false;}

template<class T1, class T2>
    bool minimize(T1 &a, T2 b){if(a > b){a = b; return true;} return false;}

template<class T1, class T2>
    void add(T1 &a, T2 b){a += b; if(a >= MOD) a -= MOD;}

template<class T1, class T2>
    void sub(T1 &a, T2 b){a -= b; if(a < 0) a += MOD;}

template<class T>
    void cps(T &v){sort(ALL(v)); v.resize(unique(ALL(v)) - v.begin());}

const int MAX = 3e5 + 10;

int N, A, B;
vector<int> adj[MAX];

int calc(int x, int y, int u, int p = -1){
    vector<int> ord;
    for(int v: adj[u]){
        if(v == p || (u == x && v == y) || (u == y && v == x)) continue;
        ord.push_back(calc(x, y, v, u));
    }
    sort(ALL(ord), greater<int>());
    int ma = 0;
    for(int i = 0; i < sz(ord); i++){
        maximize(ma, i + ord[i]);
    }
    return ma + 1;
}

vector<int> path;

bool dfs(int u, int p = -1){
    bool ans = (u == B);
    for(int v: adj[u]){
        if(v == p) continue;
        ans = ans || dfs(v, u);
    }
    if(ans) path.push_back(u);
    return ans;
}

void solve(){
    cin >> N >> A >> B;
    for(int i = 1; i < N; i++){
        int u, v; cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    dfs(A);
    int l = 1, r = sz(path) - 1;
    while(l < r){
        int m = (l + r) >> 1;
        int x = path[m], y = path[m - 1];
        if(calc(x, y, A) < calc(x, y, B)){
            r = m;
        }
        else{
            l = m + 1;
        }
    }

    int ans = max(calc(path[r], path[r - 1], A), calc(path[r], path[r - 1], B));
    if(r > 1) minimize(ans, max(calc(path[r - 2], path[r - 1], A), calc(path[r - 2], path[r - 1], B)));

    cout << ans - 1 << '\n';
}

int main(){
    ios_base::sync_with_stdio(0); cin.tie(0);
//    freopen("task.inp","r",stdin);
//    freopen("task.out","w",stdout);

    solve();

    return 0;
}

• Subtask 1: 31 / 31
• Subtask 2: 69 / 69