Submission #165763

#	Time	Username	Problem	Language	Result	Execution time	Memory
165763		jovan_b	Network (BOI15_net)	C++17	100 / 100	773 ms	50284 KiB

net

#include <bits/stdc++.h>
using namespace std;
 
int ukup=0;
int leafs=0;
int leafs1=0;
vector <int> graf[500005];
bool visited[500005];
int listovi[500005];
int brlist[500005];
 
void dfs1(int v){
    visited[v] = 1;
    bool nes = 0;
    for(auto c : graf[v]){
        if(!visited[c]){dfs1(c); nes=1; brlist[v] += brlist[c];}
    }
    if(nes == 0) {leafs++; brlist[v] = 1;}
}
 
void dfs3(int v){
    visited[v] = 1;
    bool nes = 0;
    for(auto c : graf[v]){
        if(!visited[c]){dfs3(c); nes=1;}
    }
    if(nes == 0){leafs++; listovi[leafs] = v;}
}
 
int main(){
    ios_base::sync_with_stdio(false),cin.tie(0),cerr.tie(0),cout.tie(0);
    cout.precision(10);
    cout<<fixed;
 
    int n;
    cin >> n;
    for(int i=1; i<n; i++){
        int a, b;
        cin >> a >> b;
        graf[a].push_back(b);
        graf[b].push_back(a);
    }
    if(n == 2){cout << "1\n 1 2"; return 0;}
    dfs1(1);
    int x = 1;
    for(auto c : graf[1]){
        if(brlist[c] > (brlist[1]/2)){
            x = c;
            int par;
            par = 1;
            while(1){
                if(graf[x].size() != 2) break;
                for(auto nesto : graf[x]){
                    if(nesto != par){par = x; x = nesto; break;}
                }
            }
            break;
        }
    }
    leafs = 0;
    for(int i=1; i<=n; i++) visited[i] = 0;
    dfs3(x);
    int r = 1;
    int br=0;
    while(r+(leafs/2) <= leafs){
        br++;
        r++;
    }
    r = 1;
    cout << br << "\n";
    while(r+(leafs/2) <= leafs){
        cout << listovi[r] << " " << listovi[r+(leafs/2)] << "\n";
        r++;
    }
    return 0;
}

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