이 제출은 이전 버전의 oj.uz에서 채점하였습니다. 현재는 제출 당시와는 다른 서버에서 채점을 하기 때문에, 다시 제출하면 결과가 달라질 수도 있습니다.
// header file
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
// pragma
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
// macros
#define endl "\n"
#define ll long long
#define mp make_pair
#define ins insert
#define lb lower_bound
#define pb push_back
#define ub upper_bound
#define lll __int128
#define fi first
#define se second
using namespace std;
using namespace __gnu_pbds;
typedef tree<int, null_type, less_equal<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_multiset;
typedef tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;
const int lim = 5e5 + 5;
vector<int> edges[lim];
int leafs;
bool vis[lim];
int cnt[lim];
vector<int> v;
void dfs(int nd) {
vis[nd] = 1;
cnt[nd] = 0;
if(edges[nd].size() == 1)
++cnt[nd], v.pb(nd);
for(auto i : edges[nd]) {
if(!vis[i]) {
dfs(i);
cnt[nd] += cnt[i];
}
}
}
void find_leafs(int nd) {
vis[nd] = 1;
if(edges[nd].size() ==1)
++cnt[nd];
for(auto i : edges[nd]) {
if(!vis[i])
find_leafs(i), cnt[nd] += cnt[i];
}
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(NULL);
int n;
cin >> n;
for(int i = 1; i < n; ++i) {
int u, v;
cin >> u >> v;
edges[u].pb(v), edges[v].pb(u);
}
for(int i = 1; i <= n; ++i) {
if(edges[i].size() > 1) {
find_leafs(i);
break;
}
}
pair<int, int> x = mp(1e9, 1e9);
for(int i = 1; i <= n; ++i)
if(cnt[i] >= leafs / 2)
x = min(x, mp(cnt[i], i));
// dfs from x, find left and right
memset(vis, 0, sizeof(vis));
dfs(x.se);
if((int)v.size() & 1)
v.pb(v.back());
cout << v.size() / 2 << endl;
for(int i = 0; i < v.size() / 2; ++i)
cout << v[i] << " " << v[i + v.size() / 2] << endl;
return 0;
}
컴파일 시 표준 에러 (stderr) 메시지
net.cpp: In function 'int main()':
net.cpp:75:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
75 | for(int i = 0; i < v.size() / 2; ++i)
| ~~^~~~~~~~~~~~~~
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