Submission #994590

#	Time	Username	Problem	Language	Result	Execution time	Memory
994590		guagua0407	Network (BOI15_net)	C++17	100 / 100	373 ms	47396 KiB

net

//#pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pii pair<int,int>
#define f first
#define s second
#define all(x) x.begin(),x.end()
#define _ ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);

int dx[4]={0,0,1,-1};
int dy[4]={1,-1,0,0};

void setIO(string s) {
    freopen((s + ".in").c_str(), "r", stdin);
    freopen((s + ".out").c_str(), "w", stdout);
}

const int mxn=5e5+5;
vector<int> adj[mxn];
int deg[mxn];
vector<int> vec;

void dfs(int v,int p=-1){
    for(auto u:adj[v]){
        if(u==p) continue;
        deg[v]++;
        deg[u]++;
        dfs(u,v);
    }
    if(deg[v]==1) vec.push_back(v);
}

int main() {_
    int n;
    cin>>n;
    for(int i=0;i<n-1;i++){
        int a,b;
        cin>>a>>b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    dfs(1);
    int ans=((int)vec.size()+1)/2;
    cout<<ans<<'\n';
    for(int i=0;i<ans;i++){
        cout<<vec[i]<<' '<<vec[(i+(int)vec.size()/2)]<<'\n';
    }
    return 0;
}
//maybe its multiset not set
//yeeorz
//laborz

Compilation message (stderr)

net.cpp: In function 'void setIO(std::string)':
net.cpp:15:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   15 |     freopen((s + ".in").c_str(), "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
net.cpp:16:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   16 |     freopen((s + ".out").c_str(), "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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