#include <bits/stdc++.h>
#define sz(x) ((int)x.size())
#define all(x) (x).begin(), (x).end()
#define fi first
#define se second
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
const int maxn=500000;
int n,D[maxn+10][2];
vector<int> adj[maxn+10];
vector<pii> res;
void solve(int p,int u) {
vector<int> ones,twos;
for(auto& it:adj[u]) {
if(it==p) continue;
solve(u,it);
if(D[it][1]) twos.push_back(it);
else if(D[it][0]) ones.push_back(it);
}
while(sz(twos)>=2) {
res.push_back({D[twos.back()][1],D[twos[sz(twos)-2]][1]});
ones.push_back(twos.back());
ones.push_back(twos[sz(twos)-2]);
twos.pop_back();twos.pop_back();
}
if(!twos.empty()&&ones.empty()) {
D[u][0]=D[twos[0]][0];
D[u][1]=D[twos[0]][1];
return;
}
if(!twos.empty()) {
res.push_back({D[twos.back()][1],D[ones.back()][0]});
ones.pop_back();ones.push_back(twos.back());
twos.pop_back();
}
while(sz(ones)>=3) {
res.push_back({D[ones.back()][0],D[ones[sz(ones)-2]][0]});
ones.pop_back();ones.pop_back();
}
if(u==p) {
if(sz(ones)==1) res.push_back({u,D[ones.back()][0]});
else if(sz(ones)==2) res.push_back({D[ones.back()][0],D[ones[sz(ones)-2]][0]});
} else if(sz(adj[u])==1) D[u][0]=u;
else {
if(sz(ones)>=1) D[u][0]=D[ones[0]][0];
if(sz(ones)>=2) D[u][1]=D[ones[1]][0];
}
}
int main() {
scanf("%d",&n);
int i;
for(i=0;i+1<n;i++) {
int u,v;
scanf("%d%d",&u,&v);
adj[u].push_back(v);
adj[v].push_back(u);
}
int rt=-1;
for(i=1;i<=n;i++) if(sz(adj[i])!=1) rt=i;
solve(rt,rt);
printf("%d\n",sz(res));
for(auto& it:res) printf("%d %d\n",it.fi,it.se);
return 0;
}
Compilation message
net.cpp: In function 'int main()':
net.cpp:53:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
scanf("%d",&n);
~~~~~^~~~~~~~~
net.cpp:57:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
scanf("%d%d",&u,&v);
~~~~~^~~~~~~~~~~~~~
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
12 ms |
12152 KB |
Output is correct |
2 |
Correct |
12 ms |
12024 KB |
Output is correct |
3 |
Correct |
12 ms |
12024 KB |
Output is correct |
4 |
Correct |
13 ms |
12152 KB |
Output is correct |
5 |
Correct |
12 ms |
12024 KB |
Output is correct |
6 |
Correct |
13 ms |
12152 KB |
Output is correct |
7 |
Correct |
12 ms |
12024 KB |
Output is correct |
8 |
Correct |
12 ms |
12024 KB |
Output is correct |
9 |
Correct |
12 ms |
12152 KB |
Output is correct |
10 |
Correct |
13 ms |
12024 KB |
Output is correct |
11 |
Correct |
12 ms |
12024 KB |
Output is correct |
12 |
Correct |
12 ms |
12152 KB |
Output is correct |
13 |
Correct |
12 ms |
12024 KB |
Output is correct |
14 |
Correct |
12 ms |
12024 KB |
Output is correct |
15 |
Correct |
12 ms |
12024 KB |
Output is correct |
16 |
Correct |
12 ms |
12024 KB |
Output is correct |
17 |
Correct |
12 ms |
12024 KB |
Output is correct |
18 |
Correct |
12 ms |
12024 KB |
Output is correct |
19 |
Correct |
12 ms |
12024 KB |
Output is correct |
20 |
Correct |
12 ms |
12024 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
12 ms |
12152 KB |
Output is correct |
2 |
Correct |
12 ms |
12024 KB |
Output is correct |
3 |
Correct |
12 ms |
12024 KB |
Output is correct |
4 |
Correct |
13 ms |
12152 KB |
Output is correct |
5 |
Correct |
12 ms |
12024 KB |
Output is correct |
6 |
Correct |
13 ms |
12152 KB |
Output is correct |
7 |
Correct |
12 ms |
12024 KB |
Output is correct |
8 |
Correct |
12 ms |
12024 KB |
Output is correct |
9 |
Correct |
12 ms |
12152 KB |
Output is correct |
10 |
Correct |
13 ms |
12024 KB |
Output is correct |
11 |
Correct |
12 ms |
12024 KB |
Output is correct |
12 |
Correct |
12 ms |
12152 KB |
Output is correct |
13 |
Correct |
12 ms |
12024 KB |
Output is correct |
14 |
Correct |
12 ms |
12024 KB |
Output is correct |
15 |
Correct |
12 ms |
12024 KB |
Output is correct |
16 |
Correct |
12 ms |
12024 KB |
Output is correct |
17 |
Correct |
12 ms |
12024 KB |
Output is correct |
18 |
Correct |
12 ms |
12024 KB |
Output is correct |
19 |
Correct |
12 ms |
12024 KB |
Output is correct |
20 |
Correct |
12 ms |
12024 KB |
Output is correct |
21 |
Correct |
12 ms |
12280 KB |
Output is correct |
22 |
Correct |
13 ms |
12152 KB |
Output is correct |
23 |
Correct |
13 ms |
12280 KB |
Output is correct |
24 |
Correct |
14 ms |
12152 KB |
Output is correct |
25 |
Correct |
13 ms |
12156 KB |
Output is correct |
26 |
Correct |
13 ms |
12152 KB |
Output is correct |
27 |
Correct |
13 ms |
12152 KB |
Output is correct |
28 |
Correct |
13 ms |
12152 KB |
Output is correct |
29 |
Correct |
14 ms |
12152 KB |
Output is correct |
30 |
Correct |
12 ms |
12024 KB |
Output is correct |
31 |
Correct |
13 ms |
12152 KB |
Output is correct |
32 |
Correct |
12 ms |
12024 KB |
Output is correct |
33 |
Correct |
12 ms |
12024 KB |
Output is correct |
34 |
Correct |
12 ms |
12040 KB |
Output is correct |
35 |
Correct |
12 ms |
12024 KB |
Output is correct |
36 |
Correct |
12 ms |
12024 KB |
Output is correct |
37 |
Correct |
12 ms |
12152 KB |
Output is correct |
38 |
Correct |
13 ms |
12152 KB |
Output is correct |
39 |
Correct |
12 ms |
12124 KB |
Output is correct |
40 |
Correct |
12 ms |
12024 KB |
Output is correct |
41 |
Correct |
12 ms |
12024 KB |
Output is correct |
42 |
Correct |
13 ms |
12152 KB |
Output is correct |
43 |
Correct |
13 ms |
12152 KB |
Output is correct |
44 |
Correct |
12 ms |
12024 KB |
Output is correct |
45 |
Correct |
13 ms |
12152 KB |
Output is correct |
46 |
Correct |
15 ms |
12164 KB |
Output is correct |
47 |
Correct |
12 ms |
12024 KB |
Output is correct |
48 |
Correct |
12 ms |
12152 KB |
Output is correct |
49 |
Correct |
13 ms |
12152 KB |
Output is correct |
50 |
Correct |
12 ms |
12152 KB |
Output is correct |
51 |
Correct |
12 ms |
12028 KB |
Output is correct |
52 |
Correct |
12 ms |
12152 KB |
Output is correct |
53 |
Correct |
13 ms |
12152 KB |
Output is correct |
54 |
Correct |
12 ms |
12024 KB |
Output is correct |
55 |
Correct |
12 ms |
12152 KB |
Output is correct |
56 |
Correct |
12 ms |
12024 KB |
Output is correct |
57 |
Correct |
13 ms |
12152 KB |
Output is correct |
58 |
Correct |
15 ms |
12280 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
12 ms |
12152 KB |
Output is correct |
2 |
Correct |
12 ms |
12024 KB |
Output is correct |
3 |
Correct |
12 ms |
12024 KB |
Output is correct |
4 |
Correct |
13 ms |
12152 KB |
Output is correct |
5 |
Correct |
12 ms |
12024 KB |
Output is correct |
6 |
Correct |
13 ms |
12152 KB |
Output is correct |
7 |
Correct |
12 ms |
12024 KB |
Output is correct |
8 |
Correct |
12 ms |
12024 KB |
Output is correct |
9 |
Correct |
12 ms |
12152 KB |
Output is correct |
10 |
Correct |
13 ms |
12024 KB |
Output is correct |
11 |
Correct |
12 ms |
12024 KB |
Output is correct |
12 |
Correct |
12 ms |
12152 KB |
Output is correct |
13 |
Correct |
12 ms |
12024 KB |
Output is correct |
14 |
Correct |
12 ms |
12024 KB |
Output is correct |
15 |
Correct |
12 ms |
12024 KB |
Output is correct |
16 |
Correct |
12 ms |
12024 KB |
Output is correct |
17 |
Correct |
12 ms |
12024 KB |
Output is correct |
18 |
Correct |
12 ms |
12024 KB |
Output is correct |
19 |
Correct |
12 ms |
12024 KB |
Output is correct |
20 |
Correct |
12 ms |
12024 KB |
Output is correct |
21 |
Correct |
12 ms |
12280 KB |
Output is correct |
22 |
Correct |
13 ms |
12152 KB |
Output is correct |
23 |
Correct |
13 ms |
12280 KB |
Output is correct |
24 |
Correct |
14 ms |
12152 KB |
Output is correct |
25 |
Correct |
13 ms |
12156 KB |
Output is correct |
26 |
Correct |
13 ms |
12152 KB |
Output is correct |
27 |
Correct |
13 ms |
12152 KB |
Output is correct |
28 |
Correct |
13 ms |
12152 KB |
Output is correct |
29 |
Correct |
14 ms |
12152 KB |
Output is correct |
30 |
Correct |
12 ms |
12024 KB |
Output is correct |
31 |
Correct |
13 ms |
12152 KB |
Output is correct |
32 |
Correct |
12 ms |
12024 KB |
Output is correct |
33 |
Correct |
12 ms |
12024 KB |
Output is correct |
34 |
Correct |
12 ms |
12040 KB |
Output is correct |
35 |
Correct |
12 ms |
12024 KB |
Output is correct |
36 |
Correct |
12 ms |
12024 KB |
Output is correct |
37 |
Correct |
12 ms |
12152 KB |
Output is correct |
38 |
Correct |
13 ms |
12152 KB |
Output is correct |
39 |
Correct |
12 ms |
12124 KB |
Output is correct |
40 |
Correct |
12 ms |
12024 KB |
Output is correct |
41 |
Correct |
12 ms |
12024 KB |
Output is correct |
42 |
Correct |
13 ms |
12152 KB |
Output is correct |
43 |
Correct |
13 ms |
12152 KB |
Output is correct |
44 |
Correct |
12 ms |
12024 KB |
Output is correct |
45 |
Correct |
13 ms |
12152 KB |
Output is correct |
46 |
Correct |
15 ms |
12164 KB |
Output is correct |
47 |
Correct |
12 ms |
12024 KB |
Output is correct |
48 |
Correct |
12 ms |
12152 KB |
Output is correct |
49 |
Correct |
13 ms |
12152 KB |
Output is correct |
50 |
Correct |
12 ms |
12152 KB |
Output is correct |
51 |
Correct |
12 ms |
12028 KB |
Output is correct |
52 |
Correct |
12 ms |
12152 KB |
Output is correct |
53 |
Correct |
13 ms |
12152 KB |
Output is correct |
54 |
Correct |
12 ms |
12024 KB |
Output is correct |
55 |
Correct |
12 ms |
12152 KB |
Output is correct |
56 |
Correct |
12 ms |
12024 KB |
Output is correct |
57 |
Correct |
13 ms |
12152 KB |
Output is correct |
58 |
Correct |
15 ms |
12280 KB |
Output is correct |
59 |
Correct |
507 ms |
39736 KB |
Output is correct |
60 |
Correct |
576 ms |
42828 KB |
Output is correct |
61 |
Correct |
13 ms |
12024 KB |
Output is correct |
62 |
Correct |
12 ms |
12280 KB |
Output is correct |
63 |
Correct |
454 ms |
37648 KB |
Output is correct |
64 |
Correct |
16 ms |
12792 KB |
Output is correct |
65 |
Correct |
29 ms |
15608 KB |
Output is correct |
66 |
Correct |
222 ms |
39060 KB |
Output is correct |
67 |
Correct |
710 ms |
116472 KB |
Output is correct |
68 |
Correct |
706 ms |
91452 KB |
Output is correct |
69 |
Correct |
20 ms |
13048 KB |
Output is correct |
70 |
Correct |
117 ms |
23156 KB |
Output is correct |
71 |
Correct |
373 ms |
45880 KB |
Output is correct |
72 |
Correct |
389 ms |
44580 KB |
Output is correct |
73 |
Correct |
139 ms |
20208 KB |
Output is correct |
74 |
Correct |
619 ms |
41656 KB |
Output is correct |
75 |
Correct |
42 ms |
15844 KB |
Output is correct |
76 |
Correct |
385 ms |
45548 KB |
Output is correct |
77 |
Correct |
410 ms |
45624 KB |
Output is correct |
78 |
Correct |
50 ms |
17784 KB |
Output is correct |
79 |
Correct |
675 ms |
74104 KB |
Output is correct |
80 |
Correct |
15 ms |
12408 KB |
Output is correct |
81 |
Correct |
148 ms |
23180 KB |
Output is correct |
82 |
Correct |
597 ms |
43412 KB |
Output is correct |
83 |
Correct |
633 ms |
42100 KB |
Output is correct |
84 |
Correct |
602 ms |
41716 KB |
Output is correct |
85 |
Correct |
635 ms |
41736 KB |
Output is correct |
86 |
Correct |
679 ms |
42716 KB |
Output is correct |
87 |
Correct |
602 ms |
42732 KB |
Output is correct |