Submission #538949

#	Time	Username	Problem	Language	Result	Execution time	Memory
538949		Soul234	Network (BOI15_net)	C++14	0 / 100	9 ms	12124 KiB

net

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

void DBG() { cerr << "]\n"; }
template<class H, class... T> void DBG(H h, T... t) {
    cerr << h; if(sizeof...(t)) cerr << ", ";
    DBG(t...);
}
#ifdef LOCAL
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]: [", DBG(__VA_ARGS__)
#else
#define dbg(...) 0
#endif // LOCAL

#define FOR(i,a,b) for(int i = (a) ; i<(b) ; i++)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for(int i = (b)-1 ; i>=(a) ; i--)
#define R0F(i,a) ROF(i,0,a)
#define each(e,a) for(auto &e : (a))
#define sz(v) (int)(v).size()
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define pb push_back
#define tcT template<class T
#define nl "\n"

using ll = long long;
using vi = vector<int>;
using pi = pair<int,int>;
using str = string;
tcT> using V = vector<T>;
tcT> using pqg = priority_queue<T,vector<T>,greater<T>>;

void setIO(string NAME = "") {
    cin.tie(0)->sync_with_stdio(0);
    if(sz(NAME)) {
        freopen((NAME + ".inp").c_str(),"r",stdin);
        freopen((NAME + ".out").c_str(),"w",stdout);
    }
}

const int MX = 5e5+5;

int N;
vi adj[MX];
vi lfs;
bitset<MX> isleaf;


void solve() {
    isleaf.reset();
    cin>>N;
    F0R(i,N-1) {
        int u,v;
        cin>>u>>v;
        adj[u].pb(v);
        adj[v].pb(u);
    }
    FOR(i,1,N+1) if(sz(adj[i]) == 1) isleaf[i] = 1, lfs.pb(i);
    if(sz(lfs)&1) {
        cout << sz(lfs)/2+1 << nl;
        F0R(i,sz(lfs)/2) {
            cout << lfs[i] << " " << lfs[i+sz(lfs)/2+1] << nl;
        }
        FOR(i,1,N+1) if(!isleaf[i]) {
            cout << i << " " << lfs[sz(lfs)/2] << nl;
            break;
        }
    }
    else {
        cout << sz(lfs)/2 << nl;
        F0R(i,sz(lfs)/2) {
            cout << lfs[i] << " " << lfs[i+sz(lfs)/2] << nl;
        }
    }
}

int main() {
    setIO();

    int t=1;
    //cin>>t;
    while(t-->0) {
        solve();
    }

    return 0;
}

Compilation message (stderr)

net.cpp: In function 'void setIO(std::string)':
net.cpp:37:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   37 |         freopen((NAME + ".inp").c_str(),"r",stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
net.cpp:38:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   38 |         freopen((NAME + ".out").c_str(),"w",stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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