Submission #710862

#	Time	Username	Problem	Language	Result	Execution time	Memory
710862		Charizard2021	Network (BOI15_net)	C++17	0 / 100	12 ms	23792 KiB

net

#include<bits/stdc++.h>
using namespace std;
const int N = 500001;
bool visited[N];
int LeavesInsubtee[N];
vector<int> adj[N];
vector<int> res[N];
int n;
int ans = 0;
int subtreeValue = 0;
void dfs(int u){
    visited[u] = true;
    if((int)adj[u].size() == 1){
        LeavesInsubtee[u] = 1;
    }
    for(int v : adj[u]){
        if(!visited[v]){
            dfs(v);
            LeavesInsubtee[u] += LeavesInsubtee[v];
        }
    }
}
void dfs2(int u){
    visited[u] = true;
    if((int)adj[u].size() == 1){
        res[subtreeValue].push_back(u);
    }
    for(int v : adj[u]){
        if(!visited[v]){
            dfs2(v);
        }
    }
}
int cutlocation(int u){
    visited[u] = true;
    for(int v : adj[u]){
        if(!visited[v]){
            if(LeavesInsubtee[v] > floor((ans * 2 + 1)/2)){
                return cutlocation(v);
            }
        }
    }
    return u;
}
int cut(int u){
    dfs(1);
    for(int i = 1; i <= n; i++){
        visited[i] = false;
    }
    int x = cutlocation(1);
    for(int i = 1; i <= n; i++){
        visited[i] = false;
    }
    visited[x] = true;
    for(int v : adj[x]){
        subtreeValue++;
        dfs2(v);
    }
    return x;
}
int main(){
    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);
    }
    for(int i = 1; i <= n; i++){
        if((int)adj[i].size() == 1){
            ans++;
        }
    }
    ans = (ans + 1)/2;
    cout << ans << "\n";
    cut(n);
    vector<int> finalAns(2 * ans);
    int idx = 0;
    for(int i = 1; i <= subtreeValue; i++){
        for(int j = 0; j < (int)res[i].size(); j++){
            finalAns[idx] = res[i][j];
            idx += 2;
            if(idx == 2 * ans){
                idx = 1;
            }
        }
    }
    if(!(finalAns.empty()) && finalAns.back() == 0){
        finalAns.back() = res[1][0];
    }
    for(int i = 0; i < (int)finalAns.size(); i += 2){
        cout << finalAns[i] << " " << finalAns[i + 1] << "\n";
    }
}

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