Submission #821955

#	Time	Username	Problem	Language	Result	Execution time	Memory
821955		exodus_	Network (BOI15_net)	C++14	0 / 100	8 ms	12092 KiB

net

#include<bits/stdc++.h>
#define fi first
#define se second
using namespace std;
const int nmax = 500005;
vector<int>adj[nmax];
bool leaf[nmax]={0};
bool vis[nmax]={0};
vector<pair<int,int>>dist;
vector<pair<int,int>>daft;
void dfs(int x) {
    stack<pair<int,int>>st;
    st.push({x,1});
    while(!st.empty()) {
        int nod = st.top().fi;
        int dis = st.top().se;
        vis[nod]=true;
        if(leaf[nod]==true) {
            dist.push_back({dis,nod});
        }
        st.pop();
        for(auto it:adj[nod]) {
            if(vis[it]==false) {
                st.push({it, dis+1});
            }
        }
    }
    return;
}
int main() {
    int n,a,b;
    cin >> n;
    for(int i=1; i<n; i++) {
        cin >> a >> b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    int random = -1;
    for(int i=1; i<=n; i++) {
        if(adj[i].size()==1) {
            leaf[i]=true;
            if(random==-1) random = i;
        }
    }
    dfs(random);
    sort(dist.begin(), dist.end());
    int mid = dist.size()/2;
    cout << (dist.size()+1)/2 << endl;
    for(int i=0; i<mid; i++) {
        cout << dist[i].se << " " << dist[i+mid].se << endl;
    }
    if(dist.size()%2==1) {
        cout << dist[0].se << " " << dist[dist.size()-1].se << endl;
    }
    return 0;
}

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