Submission #1128891

#TimeUsernameProblemLanguageResultExecution timeMemory
1128891ntdaccodeNetwork (BOI15_net)C++20
0 / 100
16 ms23876 KiB
#include<bits/stdc++.h> #define fori(i,a,b) for(int i=a;i<=b;i++) #define int long long #define pb push_back using namespace std; typedef pair<int,int> ii; typedef tuple<int,int,int> tp; const int M = 1e6 + 10; const int N = 1e3 + 10; const int mod = 1e9 + 7; int n; vector<int> ke[M], node; //vector<ii> ans; //namespace trace //{ // bool d[M]; // void check() // { // for(ii v : ans) { // ke[v.first].pb(v.second); // ke[v.second].pb(v.first); // } // for(int i = 1;i <= n; i++) { // d[i] = false; // } // queue<int> q; // d[1] = true; // q.push(1); // while(!q.empty()) { // int u = q.front(); q.pop(); // for(int v : ke[u]) { // if(!d[v]) { // d[v] = true; // q.push(v); // } // } // } // bool ok = 1; // for(int i = 1;i <= n; i++) if(!d[i]) ok = 0; // assert(ok); // } // //} void dfs(int u,int p = 0) { int chk = 0; for(int v : ke[u]) { if(v == p) continue; chk++; dfs(v,u); } if(chk == 1 && u == 1) node.pb(u); if(chk == 0) node.pb(u); } int32_t main() { ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); if(fopen("1.inp","r")) { freopen("1.inp","r",stdin); freopen("1.out","w",stdout); } #define task "" if(fopen(task".inp","r")) { freopen(task".inp","r",stdin); freopen(task".out","w",stdout); } cin >> n; for(int i = 1;i <= n - 1; i++) { int u, v; cin >> u >> v; ke[u].pb(v); ke[v].pb(u); } dfs(1,0); cout << (node.size() + 1)/2 << "\n"; for(int i = 0;i < node.size() - 1; i+= 2) { cout << node[i] << " " << node[i + 1] << "\n"; //ans.pb({node[i], node[i + 1]}); } if(node.size() % 2 == 1) { cout << node[0] << " " << node.back() << "\n"; //ans.pb({node[0], node.back()}); } //trace :: check(); }

Compilation message (stderr)

net.cpp: In function 'int32_t main()':
net.cpp:67:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   67 |     freopen("1.inp","r",stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~
net.cpp:68:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   68 |     freopen("1.out","w",stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~
net.cpp:73:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   73 |     freopen(task".inp","r",stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
net.cpp:74:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   74 |     freopen(task".out","w",stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
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