Submission #546153

#	Time	Username	Problem	Language	Result	Execution time	Memory
546153		OttoTheDino	Network (BOI15_net)	C++17	0 / 100	8 ms	12064 KiB

net

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

#define rep(i,s,e)                  for (int i = s; i <= e; ++i)
#define rrep(i,s,e)                 for (int i = s; i >= e; --i)
#define pb                          push_back
#define pf                          push_front
#define fi                          first
#define se                          second
#define all(a)                      a.begin(), a.end()
#define SZ(a)                       (int)a.size()
typedef long long ll;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef vector<int> vi;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;

const int mx = 5e5;
vector<vi> leafpads;
vi cur, adj[mx];
int cnt = 0, x;

void dfs (int u, int p) {
    if (SZ(adj[u])==1) {
        cur.pb(u);
        ++cnt;
    }

    for (int v : adj[u]) {
        if (v==p) continue;
        dfs (v, u);
        if (u==x) {
            leafpads.pb(cur);
            cur.clear();
        }
    }
}

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);

    int n; cin >> n;
    rep (i,1,n-1) {
        int u, v; cin >> u >> v;
        adj[u].pb(v);
        adj[v].pb(u);
    }

    rep (i,1,n) {
        if (SZ(adj[i])>1) {
            x = i;
            dfs (i,-1);
            break;
        }
    }

    cout << (cnt+1)/2 << "\n";

    sort(all(leafpads), [&](const vi a, const vi b) {
        if (SZ(b)<SZ(a)) return 1;
        return 0;
    });

    int m = SZ(leafpads);

    for (int i = 0; i < m; i += 2) {
        if (i==m-1 && leafpads[0].empty()) break;
        int u = leafpads[i].back();
        int v = leafpads[(i+1)%m].back();
        cout << u << " " << v << "\n";
        leafpads[i].pop_back();
        leafpads[(i+1)%m].pop_back();
    }

    int leafover = -1;

    rep (i,0,m-1) {
        while (SZ(leafpads[i])>1) {
            int e[2];
            rep (j,0,1) {
                e[j] = leafpads[i].back();
                leafpads[i].pop_back();
            }
            cout << e[0] << " " << e[1] << "\n";
        }
        if (!leafpads[i].empty()) {
            if (leafover==-1) leafover = leafpads[i].back();
            else {
                cout << leafover << " " << leafpads[i].back() << "\n";
                leafover = -1;
            }
        }
    }

    if (leafover!=-1) cout << leafover << " " << x << "\n";

    return 0;
}

• Subtask 1: 0 / 18
• Subtask 2: 0 / 45
• Subtask 3: 0 / 37