#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define FFOR(i,a,b,c) for(int i=(a);(c)>0?i<=(b):i>=(b);i+=(c))
#define FOOR(i,a,b) FFOR(i,a,(b)-1,1)
#define ROOF(i,a,b) FFOR(i,(b)-1,a,-1)
#define FOR(i,n) FOOR(i,0,n)
#define ROF(i,n) ROOF(i,0,n)
#define FORR(x,v) for(auto &x:v)
#define vc vector
#define sz(v) (int)((v).size())
#define bg begin()
#define en end()
#define em empty()
#define lb lower_bound
#define ub upper_bound
#define pb push_back
#define ppb pop_back()
#define eb emplace_back
#define bk back()
#define fr front()
#define pp pop()
#define all(v) (v).begin(),(v).end()
#define lla(v) (v).rbegin(),(v).rend()
#define f first
#define s second
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int N,M;
cin>>N>>M;
vc<int> bot(M),top(M),x(N,-1),y(N),free;
FOR(i,M){
cin>>bot[i]>>top[i];
bot[i]--,top[i]--;
if(bot[i]!=-1) (x[bot[i]]==-1?x[bot[i]]:y[bot[i]])=i*2;
if(top[i]!=-1) (x[top[i]]==-1?x[top[i]]:y[top[i]])=i*2+1;
if(bot[i]==-1&&top[i]==-1) free.pb(i);
}
vc<pair<int,int>> ans;
auto move=[&](int u,int v) {
ans.eb(u,v);
int a;
if(top[u]!=-1){
a=top[u];
top[u]=-1;
}else{
a=bot[u];
bot[u]=-1;
}
if(bot[v]==-1){
(x[a]/2==u?x[a]:y[a])=v*2;
bot[v]=a;
}else{
(x[a]/2==u?x[a]:y[a])=v*2+1;
top[v]=a;
}
if(bot[u]==-1){
free.pb(u);
}
};
auto park=[&](int i){
int a=x[i]/2;
int b=y[i]/2;
if(a==b)return;
if(top[a]!=-1&&top[b]!=-1) return;
if(x[i]%2==1&&y[i]%2==1) return;
if(x[i]%2==0&&top[a]!=-1) return;
if(y[i]%2==0&&top[b]!=-1) return;
if(top[b]!=-1) swap(a,b);
move(a,b);
};
auto get=[&](){
if(free.em){
cout<<-1;
exit(0);
}
int t=free.bk;
free.ppb;
return t;
};
FOR(i,M){
if(top[i]==-1&&bot[i]!=-1){
int j=i,k=bot[i];
while(x[k]%2!=y[k]%2){
j^=(x[k]/2)^(y[k]/2);
park(k);
k=bot[j];
}
}
}
FOR(i,N) park(i);
vc<bool> vis(M);
FOR(i,M){
if(vis[i]||bot[i]==top[i]||top[i]!=-1)continue;
vis[i]=1;
int k=bot[i],f=0,j=i^(x[k]/2)^(y[k]/2);
vc<int> S{k};
vc<vc<int>> T;
while(1){
T.pb({});
vis[j]=1;
k=f?bot[j]:top[j];
while(k!=-1&&x[k]%2!=y[k]%2){
T.bk.pb(k);
j^=(x[k]/2)^(y[k]/2);
vis[j]=1;
k=f?bot[j]:top[j];
}
if (k==-1)break;
S.pb(k);
j^=(x[k]/2)^(y[k]/2);
f^=1;
}
FFOR(j,1,sz(S)-2,2){
int t=get();
move(x[S[j]]/2,t);
move(y[S[j]]/2,t);
ROF(k,sz(T[j-1])) park(T[j-1][k]);
FOR(k,sz(T[j])) park(T[j][k]);
park(S[j-1]);
}
park(S.bk);
}
FOR(i,M){
if(vis[i]||bot[i]==top[i])continue;
vis[i]=1;
int k=bot[i],f=0,j=i;
vc<int> S{k};
vc<vc<int>> T;
while(1){
T.pb({});
vis[j]=1;
k=f?bot[j]:top[j];
while(k!=bot[i]&&x[k]%2!=y[k]%2){
T.bk.pb(k);
j^=(x[k]/2)^(y[k]/2);
vis[j]=1;
k=f?bot[j]:top[j];
}
if (k==bot[i])break;
S.pb(k);
j^=(x[k]/2)^(y[k]/2);
f^=1;
}
if (sz(S)==1){
int t=get();
int a=x[S[0]];
int b=y[S[0]];
if (a%2==0) swap(a,b);
move(a/2,t);
ROF(j,sz(T[0])) park(T[0][j]);
move(b/2,t);
continue;
}
int t=get();
move(x[S[1]]/2,t);
move(y[S[1]]/2,t);
ROF(j,sz(T[0])) park(T[0][j]);
FOR(j,sz(T[1])) park(T[1][j]);
FFOR(j,3,sz(S)-1,2){
int t=get();
move(x[S[j]]/2,t);
move(y[S[j]]/2,t);
ROF(k,sz(T[j-1])) park(T[j-1][k]);
FOR(k,sz(T[j])) park(T[j][k]);
park(S[j-1]);
}
park(S[0]);
if(sz(S)%2){
ROF(j,sz(T.bk)) park(T.bk[j]);
park(S.bk);
}
}
cout<<sz(ans)<<"\n";
for(auto[x,y]:ans){
cout<<x+1<<" "<<y+1<<"\n";
}
return 6/22;
}
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
0 ms |
212 KB |
Output is correct |
2 |
Correct |
0 ms |
212 KB |
Output is correct |
3 |
Correct |
0 ms |
212 KB |
Output is correct |
4 |
Correct |
0 ms |
212 KB |
Output is correct |
5 |
Correct |
1 ms |
212 KB |
Output is correct |
6 |
Correct |
0 ms |
212 KB |
Output is correct |
7 |
Correct |
0 ms |
212 KB |
Output is correct |
8 |
Correct |
0 ms |
212 KB |
Output is correct |
9 |
Correct |
0 ms |
212 KB |
Output is correct |
10 |
Correct |
0 ms |
212 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
37 ms |
4696 KB |
Output is correct |
2 |
Correct |
52 ms |
5140 KB |
Output is correct |
3 |
Correct |
31 ms |
4132 KB |
Output is correct |
4 |
Correct |
30 ms |
4044 KB |
Output is correct |
5 |
Correct |
42 ms |
5148 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
1 ms |
340 KB |
Output is correct |
2 |
Correct |
0 ms |
212 KB |
Output is correct |
3 |
Correct |
0 ms |
212 KB |
Output is correct |
4 |
Correct |
1 ms |
340 KB |
Output is correct |
5 |
Correct |
1 ms |
212 KB |
Output is correct |
6 |
Correct |
0 ms |
212 KB |
Output is correct |
7 |
Correct |
1 ms |
340 KB |
Output is correct |
8 |
Correct |
0 ms |
212 KB |
Output is correct |
9 |
Correct |
1 ms |
340 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
1 ms |
340 KB |
Output is correct |
2 |
Correct |
0 ms |
212 KB |
Output is correct |
3 |
Correct |
0 ms |
212 KB |
Output is correct |
4 |
Correct |
1 ms |
340 KB |
Output is correct |
5 |
Correct |
1 ms |
212 KB |
Output is correct |
6 |
Correct |
0 ms |
212 KB |
Output is correct |
7 |
Correct |
1 ms |
340 KB |
Output is correct |
8 |
Correct |
0 ms |
212 KB |
Output is correct |
9 |
Correct |
1 ms |
340 KB |
Output is correct |
10 |
Correct |
77 ms |
8548 KB |
Output is correct |
11 |
Correct |
28 ms |
3380 KB |
Output is correct |
12 |
Correct |
31 ms |
3372 KB |
Output is correct |
13 |
Correct |
67 ms |
7512 KB |
Output is correct |
14 |
Correct |
32 ms |
3436 KB |
Output is correct |
15 |
Correct |
31 ms |
3336 KB |
Output is correct |
16 |
Correct |
79 ms |
8680 KB |
Output is correct |
17 |
Correct |
31 ms |
3284 KB |
Output is correct |
18 |
Correct |
75 ms |
8220 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
1 ms |
340 KB |
Output is correct |
2 |
Correct |
0 ms |
340 KB |
Output is correct |
3 |
Correct |
1 ms |
340 KB |
Output is correct |
4 |
Correct |
1 ms |
340 KB |
Output is correct |
5 |
Correct |
1 ms |
340 KB |
Output is correct |
6 |
Correct |
1 ms |
340 KB |
Output is correct |
7 |
Correct |
0 ms |
340 KB |
Output is correct |
8 |
Correct |
1 ms |
340 KB |
Output is correct |
9 |
Correct |
1 ms |
340 KB |
Output is correct |
10 |
Correct |
1 ms |
340 KB |
Output is correct |
11 |
Correct |
1 ms |
340 KB |
Output is correct |
12 |
Correct |
1 ms |
340 KB |
Output is correct |
13 |
Correct |
0 ms |
340 KB |
Output is correct |
14 |
Correct |
0 ms |
340 KB |
Output is correct |
15 |
Correct |
0 ms |
340 KB |
Output is correct |
16 |
Correct |
1 ms |
320 KB |
Output is correct |
17 |
Correct |
0 ms |
340 KB |
Output is correct |
18 |
Correct |
1 ms |
340 KB |
Output is correct |
19 |
Correct |
1 ms |
340 KB |
Output is correct |
20 |
Correct |
1 ms |
340 KB |
Output is correct |
21 |
Correct |
0 ms |
340 KB |
Output is correct |
22 |
Correct |
1 ms |
340 KB |
Output is correct |
23 |
Correct |
1 ms |
340 KB |
Output is correct |
24 |
Correct |
1 ms |
340 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
0 ms |
212 KB |
Output is correct |
2 |
Correct |
0 ms |
212 KB |
Output is correct |
3 |
Correct |
0 ms |
212 KB |
Output is correct |
4 |
Correct |
0 ms |
212 KB |
Output is correct |
5 |
Correct |
1 ms |
212 KB |
Output is correct |
6 |
Correct |
0 ms |
212 KB |
Output is correct |
7 |
Correct |
0 ms |
212 KB |
Output is correct |
8 |
Correct |
0 ms |
212 KB |
Output is correct |
9 |
Correct |
0 ms |
212 KB |
Output is correct |
10 |
Correct |
0 ms |
212 KB |
Output is correct |
11 |
Correct |
37 ms |
4696 KB |
Output is correct |
12 |
Correct |
52 ms |
5140 KB |
Output is correct |
13 |
Correct |
31 ms |
4132 KB |
Output is correct |
14 |
Correct |
30 ms |
4044 KB |
Output is correct |
15 |
Correct |
42 ms |
5148 KB |
Output is correct |
16 |
Correct |
1 ms |
340 KB |
Output is correct |
17 |
Correct |
0 ms |
212 KB |
Output is correct |
18 |
Correct |
0 ms |
212 KB |
Output is correct |
19 |
Correct |
1 ms |
340 KB |
Output is correct |
20 |
Correct |
1 ms |
212 KB |
Output is correct |
21 |
Correct |
0 ms |
212 KB |
Output is correct |
22 |
Correct |
1 ms |
340 KB |
Output is correct |
23 |
Correct |
0 ms |
212 KB |
Output is correct |
24 |
Correct |
1 ms |
340 KB |
Output is correct |
25 |
Correct |
77 ms |
8548 KB |
Output is correct |
26 |
Correct |
28 ms |
3380 KB |
Output is correct |
27 |
Correct |
31 ms |
3372 KB |
Output is correct |
28 |
Correct |
67 ms |
7512 KB |
Output is correct |
29 |
Correct |
32 ms |
3436 KB |
Output is correct |
30 |
Correct |
31 ms |
3336 KB |
Output is correct |
31 |
Correct |
79 ms |
8680 KB |
Output is correct |
32 |
Correct |
31 ms |
3284 KB |
Output is correct |
33 |
Correct |
75 ms |
8220 KB |
Output is correct |
34 |
Correct |
1 ms |
340 KB |
Output is correct |
35 |
Correct |
0 ms |
340 KB |
Output is correct |
36 |
Correct |
1 ms |
340 KB |
Output is correct |
37 |
Correct |
1 ms |
340 KB |
Output is correct |
38 |
Correct |
1 ms |
340 KB |
Output is correct |
39 |
Correct |
1 ms |
340 KB |
Output is correct |
40 |
Correct |
0 ms |
340 KB |
Output is correct |
41 |
Correct |
1 ms |
340 KB |
Output is correct |
42 |
Correct |
1 ms |
340 KB |
Output is correct |
43 |
Correct |
1 ms |
340 KB |
Output is correct |
44 |
Correct |
1 ms |
340 KB |
Output is correct |
45 |
Correct |
1 ms |
340 KB |
Output is correct |
46 |
Correct |
0 ms |
340 KB |
Output is correct |
47 |
Correct |
0 ms |
340 KB |
Output is correct |
48 |
Correct |
0 ms |
340 KB |
Output is correct |
49 |
Correct |
1 ms |
320 KB |
Output is correct |
50 |
Correct |
0 ms |
340 KB |
Output is correct |
51 |
Correct |
1 ms |
340 KB |
Output is correct |
52 |
Correct |
1 ms |
340 KB |
Output is correct |
53 |
Correct |
1 ms |
340 KB |
Output is correct |
54 |
Correct |
0 ms |
340 KB |
Output is correct |
55 |
Correct |
1 ms |
340 KB |
Output is correct |
56 |
Correct |
1 ms |
340 KB |
Output is correct |
57 |
Correct |
1 ms |
340 KB |
Output is correct |
58 |
Correct |
79 ms |
10072 KB |
Output is correct |
59 |
Correct |
79 ms |
11036 KB |
Output is correct |
60 |
Correct |
65 ms |
9196 KB |
Output is correct |
61 |
Correct |
73 ms |
10112 KB |
Output is correct |
62 |
Correct |
31 ms |
5964 KB |
Output is correct |
63 |
Correct |
63 ms |
9796 KB |
Output is correct |
64 |
Correct |
36 ms |
5860 KB |
Output is correct |
65 |
Correct |
76 ms |
10660 KB |
Output is correct |
66 |
Correct |
83 ms |
11104 KB |
Output is correct |
67 |
Correct |
31 ms |
5596 KB |
Output is correct |
68 |
Correct |
76 ms |
10300 KB |
Output is correct |
69 |
Correct |
64 ms |
9780 KB |
Output is correct |
70 |
Correct |
32 ms |
5736 KB |
Output is correct |
71 |
Correct |
32 ms |
5860 KB |
Output is correct |
72 |
Correct |
32 ms |
5836 KB |
Output is correct |
73 |
Correct |
79 ms |
11136 KB |
Output is correct |
74 |
Correct |
32 ms |
5760 KB |
Output is correct |
75 |
Correct |
81 ms |
10868 KB |
Output is correct |
76 |
Correct |
78 ms |
11068 KB |
Output is correct |
77 |
Correct |
75 ms |
10684 KB |
Output is correct |
78 |
Correct |
32 ms |
5836 KB |
Output is correct |
79 |
Correct |
76 ms |
10700 KB |
Output is correct |
80 |
Correct |
31 ms |
5708 KB |
Output is correct |
81 |
Correct |
72 ms |
10512 KB |
Output is correct |