#include <bits/stdc++.h>
using namespace std;
#define bug(x) cout << #x << " " << x << endl;
const int maxn = 1e5 + 10;
vector<int> v, pai( maxn ), tam( maxn, 1 ), tempo( maxn, -1 );
vector<pair< int, int >> edge( maxn, pair< int, int>( -1, -1 ) );
int _a, _b;
int find( int& a ){ return (( a == pai[a] ) ? a : find(pai[a]) ); }
bool query( int& a, int& b ){
v.clear();
while( (pai[a] != a || pai[b] != b) && a != b ){
if( tempo[a] > tempo[b] ){
if( edge[a] != make_pair( -1, -1 ) ) v.push_back(a);
a = pai[a];
}
else{
if( edge[b] != make_pair( -1, -1 ) ) v.push_back(b);
b = pai[b];
}
}
return ( a == b );
}
void join( int& a, int& b, int& t ){
_a = find(a);
_b = find(b);
if( tam[_a] < tam[_b] ) swap( _a, _b );
tam[_a] += tam[_b];
pai[_b] = _a;
tempo[_b] = t;
edge[_b] = make_pair(a, b);
}
int main(){
int n, m; cin >> n >> m;
for( int i = 1; i <= n; i++ ) pai[i] = i;
int a, b;
while( m-- ){
cin >> a >> b;
if( !query( a, b ) ) join( a, b, m + 10 );
else for( int x : v ) edge[x] = make_pair( -1, -1 );
}
for( int i = 1; i <= n; i++ ){
if( edge[i] != make_pair( -1, -1 ) ) cout << edge[i].first << " " << edge[i].second << endl;
}
}
Compilation message
pipes.cpp: In function 'int main()':
pipes.cpp:43:47: error: cannot bind non-const lvalue reference of type 'int&' to an rvalue of type 'int'
43 | if( !query( a, b ) ) join( a, b, m + 10 );
| ~~~^~~~
pipes.cpp:27:33: note: initializing argument 3 of 'void join(int&, int&, int&)'
27 | void join( int& a, int& b, int& t ){
| ~~~~~^
