#include <bits/stdc++.h>
using namespace std;
bool ch[500009];
vector<pair<int, int> > graph[500009];
int b0[500009], t0[500009], b[500009], t[500009];
unordered_set<int> emp;
vector<int> color[500009];
vector<pair<int, int> > ans;
vector<int> comp, cols;
vector<pair<int, int> > res;
bool done[500009];
bool solo[500009];
int needed = 0;
void dfs(int v){
ch[v] = 1;
cols.push_back(v);
for(auto [e, u]: graph[v]){
comp.push_back(e);
if(!ch[u]){
dfs(u);
}
}
}
void makemove(int occ, int e){
//printf("from=%d to=%d\n", occ, e);
needed = min((int)emp.size(), needed);
ans.push_back(make_pair(occ, e));
if(t[occ]){
color[t[occ]].erase(find(color[t[occ]].begin(), color[t[occ]].end(), occ));
color[b[occ]].push_back(occ);
if(b[e]){
t[e] = t[occ];
t[occ] = 0;
}
else{
b[e] = t[occ];
t[occ] = 0;
emp.erase(e);
color[b[e]].push_back(e);
}
}
else{
color[b[occ]].erase(find(color[b[occ]].begin(), color[b[occ]].end(), occ));
emp.insert(occ);
if(b[e]){
t[e] = b[occ];
b[occ] = 0;
}
else{
b[e] = b[occ];
b[occ] = 0;
emp.erase(e);
color[b[e]].push_back(e);
}
}
needed = min((int)emp.size(), needed);
}
int main(){
int n, m, i, j, ans2 = 0;
bool flag = 0;
scanf("%d %d", &n, &m);
//assert(m<=4);
for(i=1; i<=m; i++){
scanf("%d %d", &b[i], &t[i]);
b0[i] = b[i];
t0[i] = t[i];
if(b[i] != t[i])
flag = 1, ans2++;
if(b[i] + t[i] == 0)
emp.insert(i);
if(t[i])
color[t[i]].push_back(i);
else if(b[i])
color[b[i]].push_back(i);
}
if(n==m){
if(flag)
printf("-1\n");
else
printf("0\n");
return 0;
}
while(1){
queue<int> q;
for(int c=1; c<=n; c++){
if(color[c].size() >= 2){
if(!t[color[c][0]] || !t[color[c][1]]){
q.push(c);
}
}
}
while(!q.empty()){
int c = q.front();
q.pop();
assert(color[c].size() >= 2);
assert(!t[color[c][0]] || !t[color[c][1]]);
if(!t[color[c][0]]){
makemove(color[c][1], color[c][0]);
done[c] = 1;
int temp = b[color[c][1]];
if(temp && !done[temp] && color[temp].size() >= 2){
q.push(temp);
}
}
else{
makemove(color[c][0], color[c][1]);
done[c] = 1;
int temp = b[color[c][0]];
if(temp && !done[temp] && color[temp].size() >= 2){
q.push(temp);
}
}
}
vector<bool> tch(n+1);
for(i=1; i<=m; i++){
if(b[i] && t[i]){
tch[b[i]] = 1;
tch[t[i]] = 1;
}
}
for(i=1; i<=n; i++){
if(!tch[i])
break;
}
if(i==n+1)
break;
}
for(i=1; i<=m; i++){
if(!t[i])
solo[b[i]] = 1;
}
//simulation
for(i=m+1; i<=2*m; i++)
emp.insert(i);
m *= 2;
for(i=1; i<=m; i++){
if(!b[i] || !t[i])
continue;
graph[b[i]].push_back(make_pair(i, t[i]));
graph[t[i]].push_back(make_pair(i, b[i]));
}
for(i=1; i<=n; i++){
assert(graph[i].size());
if(done[i] || ch[i] || graph[i][0].second == i)
continue;
comp.clear();
cols.clear();
int emp0 = emp.size();
needed = emp0;
//printf("i=%d\n", i);
dfs(i);
sort(comp.begin(), comp.end());
comp.erase(unique(comp.begin(), comp.end()), comp.end());
deque<int> qa;
for(int c: cols){
if(color[c].size() >= 2){
if(!t[color[c][0]] || !t[color[c][1]])
qa.push_front(c);
else
qa.push_back(c);
}
}
//printf("emp.size=%d\n", emp.size());
if(qa.empty()){
int occ = comp[0], e = *emp.begin();
//printf("occ=%d e=%d\n", occ, e);
makemove(occ, e);
for(int c: cols){
if(color[c].size() >= 2){
if(!t[color[c][0]] || !t[color[c][1]])
qa.push_front(c);
else
qa.push_back(c);
}
}
}
//printf("qa.size=%d\n", qa.size());
while(!qa.empty()){
//printf("qa.front=%d\n", qa.front());
if(done[qa.front()]){
qa.pop_front();
continue;
}
int from = color[qa.front()][0], to = color[qa.front()][1];
//printf("from=%d to=%d\n", from, to);
if(t[to])
swap(from, to);
if(t[to]){
if(emp.empty()){
printf("-1\n");
return 0;
}
int e = *emp.begin();
//printf("from=%d to=%d e=%d\n", from, to, e);
makemove(from, e);
makemove(to, e);
}
else{
makemove(from, to);
}
done[qa.front()] = 1;
qa.pop_front();
for(int c: {b[from], b[to]}){
if(c && color[c].size() == 2){
if(!t[color[c][0]] || !t[color[c][1]])
qa.push_front(c);
else
qa.push_back(c);
}
}
}
res.push_back(make_pair(emp0 - needed, i));
}
sort(res.begin(), res.end(), [](pair<int, int> &u, pair<int, int> &v){return u.first > v.first;});
m /= 2;
memset(ch, 0, sizeof(ch));
for(i=1; i<=n; i++)
graph[i].clear();
for(i=1; i<=m; i++){
b[i]= b0[i];
t[i] =t0[i];
}
emp.clear();
for(i=1; i<=n; i++)
color[i].clear();
ans.clear();
comp.clear();
cols.clear();
memset(done, 0, sizeof(done));
for(i=1; i<=m; i++){
b[i] = b0[i];
t[i] = t0[i];
if(b[i] != t[i])
flag = 1, ans2++;
if(b[i] + t[i] == 0)
emp.insert(i);
if(t[i])
color[t[i]].push_back(i);
else if(b[i])
color[b[i]].push_back(i);
}
if(n==m){
if(flag)
printf("-1\n");
else
printf("0\n");
return 0;
}
while(1){
queue<int> q;
for(int c=1; c<=n; c++){
if(color[c].size() >= 2){
if(!t[color[c][0]] || !t[color[c][1]]){
q.push(c);
}
}
}
while(!q.empty()){
int c = q.front();
q.pop();
assert(color[c].size() >= 2);
assert(!t[color[c][0]] || !t[color[c][1]]);
if(!t[color[c][0]]){
makemove(color[c][1], color[c][0]);
done[c] = 1;
int temp = b[color[c][1]];
if(temp && !done[temp] && color[temp].size() >= 2){
q.push(temp);
}
}
else{
makemove(color[c][0], color[c][1]);
done[c] = 1;
int temp = b[color[c][0]];
if(temp && !done[temp] && color[temp].size() >= 2){
q.push(temp);
}
}
}
vector<bool> tch(n+1);
for(i=1; i<=m; i++){
if(b[i] && t[i]){
tch[b[i]] = 1;
tch[t[i]] = 1;
}
}
for(i=1; i<=n; i++){
if(!tch[i])
break;
}
if(i==n+1)
break;
}
for(i=1; i<=m; i++){
if(!t[i])
solo[b[i]] = 1;
}
for(i=1; i<=m; i++){
if(!b[i] || !t[i])
continue;
graph[b[i]].push_back(make_pair(i, t[i]));
graph[t[i]].push_back(make_pair(i, b[i]));
}
for(auto [trash, i]: res){
//printf("i=%d\n", i);
assert(graph[i].size());
if(done[i] || ch[i] || graph[i][0].second == i)
continue;
comp.clear();
cols.clear();
int emp0 = emp.size();
needed = emp0;
//printf("i=%d\n", i);
dfs(i);
sort(comp.begin(), comp.end());
comp.erase(unique(comp.begin(), comp.end()), comp.end());
deque<int> qa;
for(int c: cols){
if(color[c].size() >= 2){
if(!t[color[c][0]] || !t[color[c][1]])
qa.push_front(c);
else
qa.push_back(c);
}
}
//printf("emp.size=%d\n", emp.size());
if(qa.empty()){
int occ = comp[0], e = *emp.begin();
//printf("occ=%d e=%d\n", occ, e);
makemove(occ, e);
for(int c: cols){
if(color[c].size() >= 2){
if(!t[color[c][0]] || !t[color[c][1]])
qa.push_front(c);
else
qa.push_back(c);
}
}
}
//printf("qa.size=%d\n", qa.size());
while(!qa.empty()){
//printf("qa.front=%d\n", qa.front());
if(done[qa.front()]){
qa.pop_front();
continue;
}
int from = color[qa.front()][0], to = color[qa.front()][1];
//printf("from=%d to=%d\n", from, to);
if(t[to])
swap(from, to);
if(t[to]){
if(emp.empty()){
printf("-1\n");
return 0;
}
int e = *emp.begin();
//printf("from=%d to=%d e=%d\n", from, to, e);
makemove(from, e);
makemove(to, e);
}
else{
makemove(from, to);
}
done[qa.front()] = 1;
qa.pop_front();
for(int c: {b[from], b[to]}){
if(c && color[c].size() == 2){
if(!t[color[c][0]] || !t[color[c][1]])
qa.push_front(c);
else
qa.push_back(c);
}
}
}
//res.push_back(make_pair(emp0 - needed, i));
}
printf("%d\n", ans.size());
for(auto [u, v]: ans){
printf("%d %d\n", u, v);
}
return 0;
}
Compilation message
Main.cpp: In function 'int main()':
Main.cpp:378:11: warning: format '%d' expects argument of type 'int', but argument 2 has type 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wformat=]
378 | printf("%d\n", ans.size());
| ~^ ~~~~~~~~~~
| | |
| int std::vector<std::pair<int, int> >::size_type {aka long unsigned int}
| %ld
Main.cpp:59:15: warning: unused variable 'j' [-Wunused-variable]
59 | int n, m, i, j, ans2 = 0;
| ^
Main.cpp:61:7: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
61 | scanf("%d %d", &n, &m);
| ~~~~~^~~~~~~~~~~~~~~~~
Main.cpp:64:8: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
64 | scanf("%d %d", &b[i], &t[i]);
| ~~~~~^~~~~~~~~~~~~~~~~~~~~~~
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
7 ms |
32856 KB |
Output is correct |
2 |
Correct |
6 ms |
32856 KB |
Output is correct |
3 |
Correct |
4 ms |
32856 KB |
Output is correct |
4 |
Correct |
5 ms |
32860 KB |
Output is correct |
5 |
Correct |
5 ms |
32860 KB |
Output is correct |
6 |
Correct |
5 ms |
32348 KB |
Output is correct |
7 |
Correct |
5 ms |
32856 KB |
Output is correct |
8 |
Correct |
6 ms |
32348 KB |
Output is correct |
9 |
Correct |
7 ms |
32348 KB |
Output is correct |
10 |
Correct |
6 ms |
32860 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
110 ms |
52224 KB |
Output is correct |
2 |
Correct |
152 ms |
53252 KB |
Output is correct |
3 |
Correct |
103 ms |
51088 KB |
Output is correct |
4 |
Correct |
87 ms |
50820 KB |
Output is correct |
5 |
Correct |
143 ms |
53480 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
6 ms |
33116 KB |
Output is correct |
2 |
Correct |
5 ms |
32604 KB |
Output is correct |
3 |
Correct |
8 ms |
32344 KB |
Output is correct |
4 |
Correct |
6 ms |
33116 KB |
Output is correct |
5 |
Correct |
7 ms |
32348 KB |
Output is correct |
6 |
Correct |
6 ms |
33112 KB |
Output is correct |
7 |
Correct |
6 ms |
33140 KB |
Output is correct |
8 |
Correct |
5 ms |
33116 KB |
Output is correct |
9 |
Correct |
6 ms |
33116 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
6 ms |
33116 KB |
Output is correct |
2 |
Correct |
5 ms |
32604 KB |
Output is correct |
3 |
Correct |
8 ms |
32344 KB |
Output is correct |
4 |
Correct |
6 ms |
33116 KB |
Output is correct |
5 |
Correct |
7 ms |
32348 KB |
Output is correct |
6 |
Correct |
6 ms |
33112 KB |
Output is correct |
7 |
Correct |
6 ms |
33140 KB |
Output is correct |
8 |
Correct |
5 ms |
33116 KB |
Output is correct |
9 |
Correct |
6 ms |
33116 KB |
Output is correct |
10 |
Correct |
241 ms |
59748 KB |
Output is correct |
11 |
Correct |
45 ms |
38520 KB |
Output is correct |
12 |
Correct |
53 ms |
38428 KB |
Output is correct |
13 |
Correct |
219 ms |
60168 KB |
Output is correct |
14 |
Correct |
55 ms |
37212 KB |
Output is correct |
15 |
Correct |
170 ms |
56284 KB |
Output is correct |
16 |
Correct |
222 ms |
60032 KB |
Output is correct |
17 |
Correct |
200 ms |
56532 KB |
Output is correct |
18 |
Correct |
239 ms |
60180 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
5 ms |
33112 KB |
Output is correct |
2 |
Correct |
6 ms |
33088 KB |
Output is correct |
3 |
Correct |
5 ms |
33116 KB |
Output is correct |
4 |
Correct |
6 ms |
33116 KB |
Output is correct |
5 |
Correct |
5 ms |
32600 KB |
Output is correct |
6 |
Correct |
5 ms |
33116 KB |
Output is correct |
7 |
Correct |
6 ms |
33116 KB |
Output is correct |
8 |
Incorrect |
5 ms |
33112 KB |
Output isn't correct |
9 |
Halted |
0 ms |
0 KB |
- |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
7 ms |
32856 KB |
Output is correct |
2 |
Correct |
6 ms |
32856 KB |
Output is correct |
3 |
Correct |
4 ms |
32856 KB |
Output is correct |
4 |
Correct |
5 ms |
32860 KB |
Output is correct |
5 |
Correct |
5 ms |
32860 KB |
Output is correct |
6 |
Correct |
5 ms |
32348 KB |
Output is correct |
7 |
Correct |
5 ms |
32856 KB |
Output is correct |
8 |
Correct |
6 ms |
32348 KB |
Output is correct |
9 |
Correct |
7 ms |
32348 KB |
Output is correct |
10 |
Correct |
6 ms |
32860 KB |
Output is correct |
11 |
Correct |
110 ms |
52224 KB |
Output is correct |
12 |
Correct |
152 ms |
53252 KB |
Output is correct |
13 |
Correct |
103 ms |
51088 KB |
Output is correct |
14 |
Correct |
87 ms |
50820 KB |
Output is correct |
15 |
Correct |
143 ms |
53480 KB |
Output is correct |
16 |
Correct |
6 ms |
33116 KB |
Output is correct |
17 |
Correct |
5 ms |
32604 KB |
Output is correct |
18 |
Correct |
8 ms |
32344 KB |
Output is correct |
19 |
Correct |
6 ms |
33116 KB |
Output is correct |
20 |
Correct |
7 ms |
32348 KB |
Output is correct |
21 |
Correct |
6 ms |
33112 KB |
Output is correct |
22 |
Correct |
6 ms |
33140 KB |
Output is correct |
23 |
Correct |
5 ms |
33116 KB |
Output is correct |
24 |
Correct |
6 ms |
33116 KB |
Output is correct |
25 |
Correct |
241 ms |
59748 KB |
Output is correct |
26 |
Correct |
45 ms |
38520 KB |
Output is correct |
27 |
Correct |
53 ms |
38428 KB |
Output is correct |
28 |
Correct |
219 ms |
60168 KB |
Output is correct |
29 |
Correct |
55 ms |
37212 KB |
Output is correct |
30 |
Correct |
170 ms |
56284 KB |
Output is correct |
31 |
Correct |
222 ms |
60032 KB |
Output is correct |
32 |
Correct |
200 ms |
56532 KB |
Output is correct |
33 |
Correct |
239 ms |
60180 KB |
Output is correct |
34 |
Correct |
5 ms |
33112 KB |
Output is correct |
35 |
Correct |
6 ms |
33088 KB |
Output is correct |
36 |
Correct |
5 ms |
33116 KB |
Output is correct |
37 |
Correct |
6 ms |
33116 KB |
Output is correct |
38 |
Correct |
5 ms |
32600 KB |
Output is correct |
39 |
Correct |
5 ms |
33116 KB |
Output is correct |
40 |
Correct |
6 ms |
33116 KB |
Output is correct |
41 |
Incorrect |
5 ms |
33112 KB |
Output isn't correct |
42 |
Halted |
0 ms |
0 KB |
- |