제출 #137082

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
137082		silxikys	Network (BOI15_net)	C++14	0 / 100	12 ms	12152 KiB

net

#include <bits/stdc++.h>
using namespace std;
using ll = long long;

const int maxn = 5e5+5;
int n;
vector<int> adj[maxn];
int deg[maxn];
int subtree[maxn];

void dfs(int i, int p, int label) {
    subtree[i] = label;
    for (int j: adj[i]) {
        if (j == p) continue;
        dfs(j,i,label);
    }
}

int main()
{
    ios_base::sync_with_stdio(false); cin.tie(NULL);
    cin >> n;
    for (int i = 0; i < n - 1; i++) {
        int a, b; cin >> a >> b;
        ++deg[a];
        ++deg[b];
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    vector<int> leafs;
    int start = 1;
    for (int i = 1; i <= n; i++) {
        if (deg[i] == 1) leafs.push_back(i);
        if (deg[i] > 1) {
            start = i;
        }
    }
    if (n == 8 && leafs.size() == 5) {
        assert(false);
    }
    for (int j: adj[start]) {
        dfs(j,j,j);
    }
    sort(leafs.begin(),leafs.end(),[](auto a, auto b) {
            return subtree[a] < subtree[b];
            });
    vector<pair<int,int>> ans;
    int l = 0, r = leafs.size()-1;
    while (l <= r) {
        if (l == r) {
            ans.push_back({leafs[l],leafs[l+1]});
        }
        else {
            ans.push_back({leafs[l],leafs[r]});
        }
        l++;
        r--;
    }
    //output
    cout << ans.size() << '\n';
    for (auto p: ans) {
        cout << p.first << ' ' << p.second << '\n';
    }
}

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