Submission #436724

#	Time	Username	Problem	Language	Result	Execution time	Memory
436724		ak2006	Network (BOI15_net)	C++14	100 / 100	706 ms	51576 KiB

net

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vb = vector<bool>;
using vvb = vector<vb>;
using vi = vector<int>;
using vvi = vector<vi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vc = vector<char>;
using vvc = vector<vc>;
using vs = vector<string>;
const ll mod = 1e9 + 7,inf = 1e18;
#define pb push_back
#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
void setIO()
{
    fast;
}
int n = 5e5 + 5,t;
vvi adj(n);
vi in(n),out(n),leaves;
void dfs(int u,int p)
{
    in[u] = ++t;
    for (int v:adj[u])if (v != p)
        dfs(v,u);
    out[u] = ++t;
    if (adj[u].size() == 1)leaves.pb(u);//leaves includes the root
}
bool cmp(int a,int b)
{
    return in[a] < in[b];
}
int main()
{
    setIO();
    cin>>n;
    for (int i = 0;i<n - 1;i++){int u,v;cin>>u>>v;adj[u].pb(v),adj[v].pb(u);}
    dfs(1,-1);
    sort(leaves.begin(),leaves.end(),cmp);
    int ans = (int)leaves.size();
    ans = (ans%2 == 1 ? ans/2 + 1 : ans/2);
    cout<<ans<<'\n';
    for (int i = 0;i<(int)leaves.size()/2;i++)
        cout<<leaves[i]<<" "<<leaves[(i + ans)%(int)leaves.size()]<<'\n';
    if ((int)leaves.size()%2 == 1)
        cout<<leaves[(int)leaves.size()/2]<<" "<<leaves[0];
    return 0;
}

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