#include<bits/stdc++.h>
using namespace std;
const long long inf = (long long) 1e18 + 10;
const int inf1 = (int) 1e9 + 10;
#define int long long
#define dbl long double
#define endl '\n'
#define sc second
#define fr first
#define mp make_pair
#define pb push_back
#define all(x) x.begin(), x.end()
const int maxn = 2e5+10;
int n, m, b[maxn], t[maxn], done[maxn], mark[maxn], rec[maxn];
vector<int> gin[maxn], got[maxn], need[maxn], has[maxn], pos[maxn], ept;
vector<pair<int,int>> ans;
void add(vector<int> &vec, int x) {
for(auto v : vec) if(v == x) return;
vec.pb(x);
}
void remove(vector<int> &vec, int x) {
vector<int> newv;
for(auto v : vec) if(v != x) newv.pb(v);
vec = newv;
}
void dfs(int u) {
mark[u] = 1;
rec[u] = 1;
if(got[u].size() == 2) {
add(need[u],u);
}
for(auto v : gin[u]) {
if(rec[v]) {
}
else {
if(!mark[v]) dfs(v);
for(auto x : need[v]) add(need[u],x);
}
}
rec[u] = 0;
}
void solve() {
cin >> n >> m;
for(int i = 1; i <= m; i++) {
cin >> b[i] >> t[i];
if(b[i] != 0) pos[b[i]].pb(i);
if(t[i] != 0) pos[t[i]].pb(i+m);
if(b[i] == 0) {
ept.pb(i);
}
else if(b[i] == t[i]) {
done[b[i]] = 1;
}
else if(t[i] != 0) {
got[t[i]].pb(b[i]);
gin[b[i]].pb(t[i]);
}
}
for(int i = 1; i <= n; i++) {
if(!mark[i]) dfs(i);
}
priority_queue<pair<int,int>, vector<pair<int,int>>, greater<pair<int,int>>> pq;
for(int i = 1; i <= n; i++) {
if(got[i].size() == 0) {
pq.push(mp(need[i].size(),i));
}
for(auto x : need[i]) {
has[x].pb(i);
}
}
queue<int> q;
for(int i = 1; i <= n; i++) {
if(!done[i] && gin[i].size() == 0 && got[i].size() != 2) {
q.push(i);
}
}
while(pq.size()) {
int i = pq.top().sc; pq.pop();
if(done[i]) continue;
if(ept.size() < need[i].size()) {
cout << -1 << endl;
return;
}
for(auto v : need[i]) {
sort(all(pos[v]));
int p1 = pos[v][0]-m;
int p2 = pos[v][1]-m;
int e = ept.back(); ept.pop_back();
ans.pb(mp(p1,e));
t[p1] = 0;
b[e] = v;
pos[v][0] = e;
ans.pb(mp(p2,e));
t[p2] = 0;
t[e] = v;
pos[v][1] = e+m;
done[v] = 1;
for(auto x : got[v]) {
remove(gin[x],v);
if(gin[x].size() == 0) {
q.push(x);
}
}
for(auto x : has[v]) {
remove(need[x],v);
if(got[x].size() == 0) pq.push(mp(need[x].size(),x));
}
}
while(q.size()) {
int v = q.front(); q.pop(); if(done[v]) continue;
if(got[v].size() == 1) {
sort(all(pos[v]));
int p1 = pos[v][0];
int p2 = pos[v][1]-m;
ans.pb(mp(p2,p1));
t[p2] = 0;
t[p1] = v;
pos[v][1] = p1+m;
done[v] = 1;
for(auto x : got[v]) {
remove(gin[x],v);
if(gin[x].size() == 0) {
q.push(x);
}
}
}
else {
sort(all(pos[v]));
int p1 = pos[v][0];
int p2 = pos[v][1];
ans.pb(mp(p2,p1));
b[p2] = 0;
ept.pb(p2);
t[p1] = v;
pos[v][1] = p1+m;
done[v] = 1;
for(auto x : got[v]) {
remove(gin[x],v);
if(gin[x].size() == 0) {
q.push(x);
}
}
}
}
}
//solve cycles
for(int i = 1; i <= n; i++) {
if(!done[i]) {
if(ept.size() < 1) {
cout << -1 << endl;
return;
}
queue<int> q;
sort(all(pos[i]));
int p1 = pos[i][0];
int p2 = pos[i][1]-m;
int e = ept.back(); ept.pop_back();
ans.pb(mp(p2,e));
t[p2] = 0;
b[e] = i;
pos[i][1] = e;
remove(got[i],b[p2]);
remove(gin[b[p2]],i);
if(gin[b[p2]].size() == 0) {
q.push(b[p2]);
}
while(q.size()) {
int v = q.front(); q.pop();
if(got[v].size() == 1) {
sort(all(pos[v]));
int p1 = pos[v][0];
int p2 = pos[v][1]-m;
ans.pb(mp(p2,p1));
t[p2] = 0;
t[p1] = v;
pos[v][1] = p1+m;
done[v] = 1;
for(auto x : got[v]) {
remove(gin[x],v);
if(gin[x].size() == 0) {
q.push(x);
}
}
}
else {
sort(all(pos[v]));
int p1 = pos[v][0];
int p2 = pos[v][1];
ans.pb(mp(p2,p1));
b[p2] = 0;
ept.pb(p2);
t[p1] = v;
pos[v][1] = p1+m;
done[v] = 1;
for(auto x : got[v]) {
remove(gin[x],v);
if(gin[x].size() == 0) {
q.push(x);
}
}
}
}
}
}
cout << ans.size() << endl;
for(auto x : ans) {
cout << x.fr << " " << x.sc << endl;
}
}
int32_t main() {
ios::sync_with_stdio(false); cin.tie(0);
// freopen("in.in", "r", stdin);
// freopen("out.out", "w", stdout);
int tt = 1;
// cin >> tt;
while(tt--) {
solve();
}
}
Compilation message
Main.cpp: In function 'void solve()':
Main.cpp:177:17: warning: unused variable 'p1' [-Wunused-variable]
177 | int p1 = pos[i][0];
| ^~
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
14 ms |
23764 KB |
Output is correct |
2 |
Correct |
12 ms |
23744 KB |
Output is correct |
3 |
Correct |
14 ms |
23764 KB |
Output is correct |
4 |
Correct |
13 ms |
23764 KB |
Output is correct |
5 |
Correct |
14 ms |
23832 KB |
Output is correct |
6 |
Correct |
12 ms |
23764 KB |
Output is correct |
7 |
Correct |
12 ms |
23764 KB |
Output is correct |
8 |
Correct |
13 ms |
23776 KB |
Output is correct |
9 |
Correct |
12 ms |
23764 KB |
Output is correct |
10 |
Correct |
12 ms |
23764 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
104 ms |
37948 KB |
Output is correct |
2 |
Correct |
142 ms |
40988 KB |
Output is correct |
3 |
Correct |
81 ms |
35136 KB |
Output is correct |
4 |
Correct |
70 ms |
34400 KB |
Output is correct |
5 |
Correct |
141 ms |
40600 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
15 ms |
23892 KB |
Output is correct |
2 |
Correct |
15 ms |
23892 KB |
Output is correct |
3 |
Correct |
13 ms |
23964 KB |
Output is correct |
4 |
Correct |
13 ms |
24020 KB |
Output is correct |
5 |
Correct |
15 ms |
23904 KB |
Output is correct |
6 |
Correct |
15 ms |
23892 KB |
Output is correct |
7 |
Correct |
16 ms |
24020 KB |
Output is correct |
8 |
Correct |
13 ms |
23948 KB |
Output is correct |
9 |
Correct |
15 ms |
24020 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
15 ms |
23892 KB |
Output is correct |
2 |
Correct |
15 ms |
23892 KB |
Output is correct |
3 |
Correct |
13 ms |
23964 KB |
Output is correct |
4 |
Correct |
13 ms |
24020 KB |
Output is correct |
5 |
Correct |
15 ms |
23904 KB |
Output is correct |
6 |
Correct |
15 ms |
23892 KB |
Output is correct |
7 |
Correct |
16 ms |
24020 KB |
Output is correct |
8 |
Correct |
13 ms |
23948 KB |
Output is correct |
9 |
Correct |
15 ms |
24020 KB |
Output is correct |
10 |
Correct |
478 ms |
64564 KB |
Output is correct |
11 |
Correct |
115 ms |
44116 KB |
Output is correct |
12 |
Correct |
308 ms |
54700 KB |
Output is correct |
13 |
Correct |
402 ms |
62340 KB |
Output is correct |
14 |
Correct |
339 ms |
58820 KB |
Output is correct |
15 |
Correct |
300 ms |
57796 KB |
Output is correct |
16 |
Correct |
464 ms |
67856 KB |
Output is correct |
17 |
Correct |
296 ms |
58276 KB |
Output is correct |
18 |
Correct |
431 ms |
65208 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
17 ms |
24000 KB |
Output is correct |
2 |
Correct |
13 ms |
23892 KB |
Output is correct |
3 |
Correct |
13 ms |
23980 KB |
Output is correct |
4 |
Correct |
12 ms |
23956 KB |
Output is correct |
5 |
Correct |
16 ms |
23832 KB |
Output is correct |
6 |
Correct |
13 ms |
23892 KB |
Output is correct |
7 |
Correct |
16 ms |
23956 KB |
Output is correct |
8 |
Correct |
13 ms |
24020 KB |
Output is correct |
9 |
Correct |
13 ms |
24020 KB |
Output is correct |
10 |
Correct |
13 ms |
23944 KB |
Output is correct |
11 |
Correct |
15 ms |
23944 KB |
Output is correct |
12 |
Correct |
13 ms |
23892 KB |
Output is correct |
13 |
Correct |
13 ms |
23892 KB |
Output is correct |
14 |
Correct |
13 ms |
23892 KB |
Output is correct |
15 |
Correct |
13 ms |
23892 KB |
Output is correct |
16 |
Correct |
14 ms |
24148 KB |
Output is correct |
17 |
Correct |
13 ms |
23892 KB |
Output is correct |
18 |
Correct |
13 ms |
24020 KB |
Output is correct |
19 |
Correct |
13 ms |
24020 KB |
Output is correct |
20 |
Correct |
12 ms |
24020 KB |
Output is correct |
21 |
Correct |
13 ms |
23936 KB |
Output is correct |
22 |
Correct |
14 ms |
24020 KB |
Output is correct |
23 |
Correct |
13 ms |
23892 KB |
Output is correct |
24 |
Correct |
15 ms |
24020 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
14 ms |
23764 KB |
Output is correct |
2 |
Correct |
12 ms |
23744 KB |
Output is correct |
3 |
Correct |
14 ms |
23764 KB |
Output is correct |
4 |
Correct |
13 ms |
23764 KB |
Output is correct |
5 |
Correct |
14 ms |
23832 KB |
Output is correct |
6 |
Correct |
12 ms |
23764 KB |
Output is correct |
7 |
Correct |
12 ms |
23764 KB |
Output is correct |
8 |
Correct |
13 ms |
23776 KB |
Output is correct |
9 |
Correct |
12 ms |
23764 KB |
Output is correct |
10 |
Correct |
12 ms |
23764 KB |
Output is correct |
11 |
Correct |
104 ms |
37948 KB |
Output is correct |
12 |
Correct |
142 ms |
40988 KB |
Output is correct |
13 |
Correct |
81 ms |
35136 KB |
Output is correct |
14 |
Correct |
70 ms |
34400 KB |
Output is correct |
15 |
Correct |
141 ms |
40600 KB |
Output is correct |
16 |
Correct |
15 ms |
23892 KB |
Output is correct |
17 |
Correct |
15 ms |
23892 KB |
Output is correct |
18 |
Correct |
13 ms |
23964 KB |
Output is correct |
19 |
Correct |
13 ms |
24020 KB |
Output is correct |
20 |
Correct |
15 ms |
23904 KB |
Output is correct |
21 |
Correct |
15 ms |
23892 KB |
Output is correct |
22 |
Correct |
16 ms |
24020 KB |
Output is correct |
23 |
Correct |
13 ms |
23948 KB |
Output is correct |
24 |
Correct |
15 ms |
24020 KB |
Output is correct |
25 |
Correct |
478 ms |
64564 KB |
Output is correct |
26 |
Correct |
115 ms |
44116 KB |
Output is correct |
27 |
Correct |
308 ms |
54700 KB |
Output is correct |
28 |
Correct |
402 ms |
62340 KB |
Output is correct |
29 |
Correct |
339 ms |
58820 KB |
Output is correct |
30 |
Correct |
300 ms |
57796 KB |
Output is correct |
31 |
Correct |
464 ms |
67856 KB |
Output is correct |
32 |
Correct |
296 ms |
58276 KB |
Output is correct |
33 |
Correct |
431 ms |
65208 KB |
Output is correct |
34 |
Correct |
17 ms |
24000 KB |
Output is correct |
35 |
Correct |
13 ms |
23892 KB |
Output is correct |
36 |
Correct |
13 ms |
23980 KB |
Output is correct |
37 |
Correct |
12 ms |
23956 KB |
Output is correct |
38 |
Correct |
16 ms |
23832 KB |
Output is correct |
39 |
Correct |
13 ms |
23892 KB |
Output is correct |
40 |
Correct |
16 ms |
23956 KB |
Output is correct |
41 |
Correct |
13 ms |
24020 KB |
Output is correct |
42 |
Correct |
13 ms |
24020 KB |
Output is correct |
43 |
Correct |
13 ms |
23944 KB |
Output is correct |
44 |
Correct |
15 ms |
23944 KB |
Output is correct |
45 |
Correct |
13 ms |
23892 KB |
Output is correct |
46 |
Correct |
13 ms |
23892 KB |
Output is correct |
47 |
Correct |
13 ms |
23892 KB |
Output is correct |
48 |
Correct |
13 ms |
23892 KB |
Output is correct |
49 |
Correct |
14 ms |
24148 KB |
Output is correct |
50 |
Correct |
13 ms |
23892 KB |
Output is correct |
51 |
Correct |
13 ms |
24020 KB |
Output is correct |
52 |
Correct |
13 ms |
24020 KB |
Output is correct |
53 |
Correct |
12 ms |
24020 KB |
Output is correct |
54 |
Correct |
13 ms |
23936 KB |
Output is correct |
55 |
Correct |
14 ms |
24020 KB |
Output is correct |
56 |
Correct |
13 ms |
23892 KB |
Output is correct |
57 |
Correct |
15 ms |
24020 KB |
Output is correct |
58 |
Correct |
388 ms |
60932 KB |
Output is correct |
59 |
Correct |
452 ms |
66560 KB |
Output is correct |
60 |
Correct |
363 ms |
55200 KB |
Output is correct |
61 |
Correct |
399 ms |
62524 KB |
Output is correct |
62 |
Correct |
108 ms |
44584 KB |
Output is correct |
63 |
Correct |
333 ms |
57196 KB |
Output is correct |
64 |
Correct |
306 ms |
58564 KB |
Output is correct |
65 |
Correct |
437 ms |
65680 KB |
Output is correct |
66 |
Correct |
465 ms |
67384 KB |
Output is correct |
67 |
Correct |
290 ms |
54348 KB |
Output is correct |
68 |
Correct |
379 ms |
62780 KB |
Output is correct |
69 |
Correct |
379 ms |
61608 KB |
Output is correct |
70 |
Correct |
291 ms |
55896 KB |
Output is correct |
71 |
Correct |
330 ms |
58508 KB |
Output is correct |
72 |
Correct |
311 ms |
58236 KB |
Output is correct |
73 |
Correct |
483 ms |
67504 KB |
Output is correct |
74 |
Correct |
323 ms |
58180 KB |
Output is correct |
75 |
Correct |
461 ms |
66304 KB |
Output is correct |
76 |
Correct |
458 ms |
67040 KB |
Output is correct |
77 |
Correct |
440 ms |
65872 KB |
Output is correct |
78 |
Correct |
332 ms |
58024 KB |
Output is correct |
79 |
Correct |
437 ms |
65588 KB |
Output is correct |
80 |
Correct |
298 ms |
58548 KB |
Output is correct |
81 |
Correct |
404 ms |
64408 KB |
Output is correct |