#include<bits/stdc++.h>
using namespace std;
#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define in insert
#define all(x) x.begin(),x.end()
#define pb push_back
#define eb emplace_back
#define ff first
#define ss second
// #define int long long
typedef long long ll;
typedef vector<int> vi;
typedef set<int> si;
typedef multiset<int> msi;
typedef pair<int, int> pii;
typedef vector<pii> vpii;
template<typename T, typename U>
ostream & operator << (ostream &out, const pair<T, U> &c) {
out << c.first << ' ' << c.second;
return out;
}
template<typename T>
ostream & operator << (ostream &out, vector<T> &v) {
const int sz = v.size();
for (int i = 0; i < sz; i++) {
if (i) out << ' ';
out << v[i];
}
return out;
}
template<typename T>
istream & operator >> (istream &in, vector<T> &v) {
for (T &x : v) in >> x;
return in;
}
template<typename T>
void mxx(T &a, T b){if(b > a) a = b;}
template<typename T>
void mnn(T &a, T b){if(b < a) a = b;}
const int mxn = 2e5 + 10;
int v[mxn][2], done[mxn], tp[mxn], tot;
vector<int> g[mxn][2];
set<int> em;
vector<pair<int, int>> ans;
void add(int x, int y) {
ans.eb(x, y);
int id1 = (v[x][1] > 0), id2 = (v[y][0] > 0);
int val = v[x][id1];
g[val][id1].erase(find(all(g[val][id1]), x));
g[val][id2].pb(y);
v[x][id1] = 0;
v[y][id2] = val;
if(id1 == 0) em.in(x);
if(id2 == 0) em.erase(y);
}
void clearTop(int x) {
if(done[x] || tp[x] != 2) return;
if(em.size() == 0) {
cout << -1 << '\n';
exit(0);
}
int emp = *em.begin();
add(g[x][1][0], emp);
add(g[x][1][1], emp);
done[x] = 1;
tot--;
}
void dfs1(int x) {
if(done[x] || tp[x] != 3) return;
if(v[g[x][0][0]][1] == 0) {
int nxt = g[x][1][0];
add(g[x][1][0], g[x][0][0]);
done[x] = 1;
tot--;
dfs1(v[nxt][0]);
}
}
void dfs2(int x) {
if(done[x] || tp[x] == 2) return;
if(tp[x] == 1) {
int x1 = g[x][0][0], x2 = g[x][0][1];
if(v[x1][1] == 0 && v[x2][1] == 0) {
add(x1, x2);
done[x] = 1;
tot--;
} else if(v[x1][1] == 0 || v[x2][1] == 0) {
int obs = max(v[x2][1], v[x1][1]);
int pos = (v[x1][1] ? x1 : x2);
if(tp[obs] != 2) return;
int nxt = g[obs][1][0] ^ g[obs][1][1] ^ pos;
nxt = v[nxt][0];
clearTop(obs);
add(x1, x2);
done[x] = 1;
tot--;
dfs2(nxt);
}
} else {
int pos = g[x][0][0], nxt = v[g[x][1][0]][0];
if(v[pos][1]) return;
add(g[x][1][0], g[x][0][0]);
done[x] = 1;
tot--;
dfs2(nxt);
}
}
void go() {
int n, m;
cin >> n >> m;
tot = n;
for(int i = 1; i <= m; i++) {
for(int j = 0; j < 2; j++) {
cin >> v[i][j];
if(v[i][j]) g[v[i][j]][j].pb(i);
}
if(v[i][0] == 0 && v[i][1] == 0) em.in(i);
}
for(int i = 1; i <= n; i++) {
if(g[i][0].size() && g[i][1].size()) tp[i] = 3;
else if(g[i][0].size()) tp[i] = 1;
else tp[i] = 2;
}
for(int i = 1; i <= n; i++) {
if(tp[i] == 3 && g[i][0][0] == g[i][1][0]) done[i] = 1;
else if(tp[i] == 1) {
int x = g[i][0][0], y = g[i][0][1];
if(v[x][1] == 0 && v[y][1] == 0) {
done[i] = 1;
add(x, y);
}
}
tot -= done[i];
}
while(tot > 0) {
for(int i = 1; i <= n; i++) {
if(done[i]) continue;
dfs1(i);
}
for(int i = 1; i <= n; i++) {
if(done[i]) continue;
dfs2(i);
}
bool found = 0;
for(int i = 1; i <= n; i++) {
if(tp[i] != 3 || done[i]) continue;
int x1 = g[i][1][0], x2 = g[i][1][1];
int val1 = v[x1][0], val2 = v[x2][0];
if(tp[val1] == 3 || tp[val2] == 3) {
clearTop(i);
found = 1;
break;
}
}
if(!found) {
for(int i = 1; i <= n; i++) {
if(tp[i] != 3 || done[i]) continue;
clearTop(i);
found = 1;
break;
}
}
if(!found) {
cout << -1 << '\n';
return;
}
}
cout << ans.size() << '\n';
for(auto it : ans) {
cout << it << '\n';
}
}
signed main() {
// #ifndef ONO
// freopen("file.in", "r", stdin);
// freopen("file.out", "w", stdout);
// #endif
fast;
int t = 1;
// cin >> t;
while(t--) {
go();
}
return 0;
}
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
4 ms |
9684 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Execution timed out |
2066 ms |
22792 KB |
Time limit exceeded |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Execution timed out |
2070 ms |
9684 KB |
Time limit exceeded |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Execution timed out |
2070 ms |
9684 KB |
Time limit exceeded |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Execution timed out |
2052 ms |
9728 KB |
Time limit exceeded |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
4 ms |
9684 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
