Submission #524743

#	Time	Username	Problem	Language	Result	Execution time	Memory
524743		perchuts	Network (BOI15_net)	C++17	18 / 100	8 ms	12108 KiB

net

#include <bits/stdc++.h>
#define maxn (int)(1e5+51)
#define all(x) x.begin(), x.end()
#define sz(x) (int) x.size()
#define endl '\n'
#define ll long long
#define pb push_back
#define ull unsigned long long
#define ii pair<int,int>
#define iii tuple<int,int,int>
#define inf 2000000001
#define mod 1000000007 //998244353
#define _ ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);

using namespace std;

template<typename X, typename Y> bool ckmin(X& x, const Y& y) { return (y < x) ? (x=y,1):0; }
template<typename X, typename Y> bool ckmax(X& x, const Y& y) { return (x < y) ? (x=y,1):0; }
vector<int>g[5*maxn];
vector<int>leaves;
void dfs(int x,int p){
    int ok = 0;
    for(auto v:g[x]){
        if(v==p)continue;
        ok = 1;
        dfs(v,x);
    }
    if(!ok||(x==1&&sz(g[x])==1))leaves.pb(x);
}
int main(){_
    int n;cin>>n;
    for(int i=1;i<n;i++){
        int a,b;cin>>a>>b;
        g[a].pb(b);
        g[b].pb(a);
    }    
    dfs(1,1);
    int x = sz(leaves);
    cout<<(x+1)/2<<endl;
    for(int i=0;i<x/2;i++)cout<<leaves[i]<<" "<<leaves[i+x/2]<<endl;
    if(x&1){
        int u = leaves[x-1],v;
        for(int i=1;i<=n;i++)if(i!=u&&i!=g[u][0])v=i;
        cout<<u<<" "<<v<<endl;
    }
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:5:14: warning: 'v' may be used uninitialized in this function [-Wmaybe-uninitialized]
    5 | #define endl '\n'
      |              ^~~~
net.cpp:42:29: note: 'v' was declared here
   42 |         int u = leaves[x-1],v;
      |                             ^

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