Submission #717510

#TimeUsernameProblemLanguageResultExecution timeMemory
717510Charizard2021Network (BOI15_net)C++17
18 / 100
25 ms35876 KiB
#include<bits/stdc++.h> using namespace std; const int N = 500001; #define IOS ios::sync_with_stdio(false);; cin.tie(NULL) bool visited[N]; int LeavesInsubtee[N]; vector<int> adj[N]; vector<int> res[N]; vector<int> v2[N]; int n; int ans = 0; int cur_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((cur_ans)/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; } struct cmp{ bool operator()(const int &a, const int &b) const{ if(res[a].size() == res[b].size()){ return a < b; } return res[a].size() > res[b].size(); } }; int main(){ // ifstream cin("net2y.in"); // ofstream cout("net2y.out"); IOS; 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++; } } cur_ans = ans; ans = (ans + 1)/2; cout << ans << "\n"; cut(n); vector<int> v; vector<int> res2[subtreeValue + 1]; for(int i = 1; i <= subtreeValue; i++){ v2[res[i].size()].push_back(i); res2[i] = res[i]; } int first_pointer = -1; int second_pointer = -1; for(int i = N - 1; i > 0; i--){ if(!v2[i].empty() && first_pointer == -1){ first_pointer = i; } if(v2[i].size() > 1 && second_pointer == -1){ second_pointer = i; } } while(first_pointer > 0){ int x = v2[first_pointer].back(); v.push_back(res[x].back()); v2[first_pointer].pop_back(); res[x].pop_back(); if(second_pointer > 0 && v2[second_pointer].size() != 0){ int y = v2[second_pointer].back(); v.push_back(res[y].back()); v2[second_pointer].pop_back(); res[y].pop_back(); if(!res[y].empty()){ v2[res[y].size()].push_back(y); } if((first_pointer == second_pointer && v2[res[y].size() + 1].size() <= 1) || (first_pointer != second_pointer && v2[res[y].size() + 1].size() == 0)){ second_pointer--; } } if(!res[x].empty()){ v2[res[x].size()].push_back(x); } if(v2[res[x].size() + 1].size() == 0){ first_pointer--; } } if(v.size() % 2 == 1){ for(int i = 1; i <= subtreeValue; i++){ for(int j = 0; j < res2[i].size(); j++){ if(res2[i][j] != v.back()){ v.push_back(res2[i][j]); break; } } if(v.size() % 2== 0){ break; } } } for(int i = 0; i < (int)v.size(); i += 2){ cout << v[i] << " " << v[i + 1] << "\n"; } }

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:134:30: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  134 |             for(int j = 0; j < res2[i].size(); j++){
      |                            ~~^~~~~~~~~~~~~~~~
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