Submission #58653

#	Time	Username	Problem	Language	Result	Execution time	Memory
58653		SpeedOfMagic	Network (BOI15_net)	C++17	100 / 100	1079 ms	89248 KiB

net

/** MIT License Copyright (c) 2018 Vasilyev Daniil **/
#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("Ofast")
template<typename T> using v = vector<T>;
#define int long long
typedef string str;
typedef vector<int> vint;
#define rep(a, l, r) for(int a = (l); a < (r); a++)
#define pb push_back
#define sz(a) ((int) a.size())
const long long inf = 4611686018427387903; //2^62 - 1
#if 0  //FileIO
const string fileName = "";
ifstream fin ((fileName == "" ? "input.txt"  : fileName + ".in" ));
ofstream fout((fileName == "" ? "output.txt" : fileName + ".out"));
#define get fin>>
#define put fout<<
#else
#define get cin>>
#define put cout<<
#endif
#define eol put endl
void read() {}     template<typename Arg,typename... Args> void read (Arg& arg,Args&... args){get (arg)     ;read(args...) ;}
void print(){}     template<typename Arg,typename... Args> void print(Arg  arg,Args...  args){put (arg)<<" ";print(args...);}
void debug(){eol;} template<typename Arg,typename... Args> void debug(Arg  arg,Args...  args){put (arg)<<" ";debug(args...);}
int getInt(){int a; get a; return a;}
//code goes here
const int N = 500001;
vint g[N];
v<pair<int, int>> ans;
vint dfs(int cur, int p = -1) {
    if (sz(g[cur]) == 1)
        return vint({cur});
    else {
        vint pos;
        for (int i : g[cur]) {
            if (i == p)
                continue;
            vint z = dfs(i, cur);

            if (sz(z) == 2 && sz(pos) == 1)
                for (int j : z)
                    if (pos.empty())
                        pos.pb(j);
                    else {
                        ans.pb({pos.back(), j});
                        pos.pop_back();
                    }
            else
                for (int j : z)
                    if (sz(pos) < 2)
                        pos.pb(j);
                    else {
                        ans.pb({pos.back(), j});
                        pos.pop_back();
                    }
        }

        if (p == -1) {
            if (sz(pos) == 2)
                ans.pb({pos[0], pos[1]});
            else if (g[pos[0]][0] != cur)
                ans.pb({pos[0], cur});
            else
                rep(i, 1, N)
                    if (pos[0] != i && g[pos[0]][0] != i) {
                        ans.pb({pos[0], i});
                        break;
                    }
        }

        return pos;
    }
}

void run() {
    int n;
    get n;
    n++;
    rep(i, 2, n) {
        int v, u;
        read(v, u);
        g[v].pb(u);
        g[u].pb(v);
    }

    rep(i, 1, n)
        if (sz(g[i]) != 1) {
            dfs(i);
            break;
        }

    put sz(ans);
    eol;
    for (auto i : ans)
        debug(i.first, i.second);
}

int32_t main() {srand(time(0)); ios::sync_with_stdio(0); cin.tie(0); cout.tie(0); put fixed; put setprecision(15); run(); return 0;}

• Subtask 1: 18 / 18
• Subtask 2: 45 / 45
• Subtask 3: 37 / 37