Submission #147130

#	Submission time	Handle	Problem	Language	Result	Execution time	Memory
147130	2019-08-27T20:45:23 Z	fadi57	Network (BOI15_net)	C++14	100 / 100	589 ms	47856 KB

/*
  problem is equivalent to: cover the tree with minimum number of paths from one node to another one
  optimal solution is to connect nodes with degree = 1
  connect leaves i and i+sz/2 where sz is size of set of the leaves
  this works because it is always possible to pick a node such that number of leaves in its subtree is sz/2
  *handle the case when sz is odd
*/

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
const ll MOD = 1e9+7;
const int N = 5e5+5;

int n;
vector<int>leaf;
vector<int>v[N];

void dfs(int s,int p){
	if(v[s].size()==1){
		leaf.push_back(s);
	}
	for(int i=0;i<v[s].size();i++){
		if(v[s][i]!=p){
			dfs(v[s][i],s);
		}
	}
}

int main() {
	ios_base::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);

	int x,y;
	cin>>n;
	for(int i=0;i<n-1;i++){
		cin>>x>>y;
		v[x].push_back(y);
		v[y].push_back(x);
	}

	dfs(1,-1);
	int k=(int)leaf.size();
	if(k%2==0){
		cout<<k/2<<"\n";
		for(int i=0;i<k/2;i++){
			cout<<leaf[i]<<" "<<leaf[i+k/2]<<"\n";
		}
	}else{
		cout<<k/2+1<<"\n";
		for(int i=0;i<k/2;i++){
			cout<<leaf[i]<<" "<<leaf[i+k/2+1]<<"\n";
		}
		cout<<leaf[k/2]<<" "<<1;
	}

	return 0;
}

Compilation message

net.cpp: In function 'void dfs(int, int)':
net.cpp:24:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<v[s].size();i++){
              ~^~~~~~~~~~~~

Subtask #1
18.0 / 18.0

#	Verdict	Execution time	Memory	Grader output
1	Correct	13 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	12 ms	12152 KB	Output is correct
5	Correct	12 ms	12108 KB	Output is correct
6	Correct	12 ms	12024 KB	Output is correct
7	Correct	12 ms	12024 KB	Output is correct
8	Correct	14 ms	12028 KB	Output is correct
9	Correct	13 ms	12152 KB	Output is correct
10	Correct	12 ms	12024 KB	Output is correct
11	Correct	12 ms	12152 KB	Output is correct
12	Correct	13 ms	12152 KB	Output is correct
13	Correct	15 ms	12100 KB	Output is correct
14	Correct	16 ms	12152 KB	Output is correct
15	Correct	15 ms	12152 KB	Output is correct
16	Correct	12 ms	12024 KB	Output is correct
17	Correct	12 ms	12152 KB	Output is correct
18	Correct	12 ms	12152 KB	Output is correct
19	Correct	12 ms	12152 KB	Output is correct
20	Correct	13 ms	12152 KB	Output is correct

Subtask #2
45.0 / 45.0

#	Verdict	Execution time	Memory	Grader output
1	Correct	13 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	12 ms	12152 KB	Output is correct
5	Correct	12 ms	12108 KB	Output is correct
6	Correct	12 ms	12024 KB	Output is correct
7	Correct	12 ms	12024 KB	Output is correct
8	Correct	14 ms	12028 KB	Output is correct
9	Correct	13 ms	12152 KB	Output is correct
10	Correct	12 ms	12024 KB	Output is correct
11	Correct	12 ms	12152 KB	Output is correct
12	Correct	13 ms	12152 KB	Output is correct
13	Correct	15 ms	12100 KB	Output is correct
14	Correct	16 ms	12152 KB	Output is correct
15	Correct	15 ms	12152 KB	Output is correct
16	Correct	12 ms	12024 KB	Output is correct
17	Correct	12 ms	12152 KB	Output is correct
18	Correct	12 ms	12152 KB	Output is correct
19	Correct	12 ms	12152 KB	Output is correct
20	Correct	13 ms	12152 KB	Output is correct
21	Correct	12 ms	12024 KB	Output is correct
22	Correct	13 ms	12280 KB	Output is correct
23	Correct	14 ms	12128 KB	Output is correct
24	Correct	16 ms	12152 KB	Output is correct
25	Correct	13 ms	12152 KB	Output is correct
26	Correct	13 ms	12152 KB	Output is correct
27	Correct	13 ms	12152 KB	Output is correct
28	Correct	16 ms	12124 KB	Output is correct
29	Correct	14 ms	12280 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	12152 KB	Output is correct
34	Correct	12 ms	12024 KB	Output is correct
35	Correct	12 ms	12152 KB	Output is correct
36	Correct	12 ms	12152 KB	Output is correct
37	Correct	12 ms	12156 KB	Output is correct
38	Correct	12 ms	12152 KB	Output is correct
39	Correct	12 ms	12024 KB	Output is correct
40	Correct	12 ms	12152 KB	Output is correct
41	Correct	12 ms	12024 KB	Output is correct
42	Correct	13 ms	12024 KB	Output is correct
43	Correct	13 ms	12168 KB	Output is correct
44	Correct	12 ms	12024 KB	Output is correct
45	Correct	12 ms	12024 KB	Output is correct
46	Correct	13 ms	12152 KB	Output is correct
47	Correct	12 ms	12152 KB	Output is correct
48	Correct	12 ms	12024 KB	Output is correct
49	Correct	13 ms	12152 KB	Output is correct
50	Correct	12 ms	12024 KB	Output is correct
51	Correct	12 ms	12024 KB	Output is correct
52	Correct	12 ms	12024 KB	Output is correct
53	Correct	12 ms	12152 KB	Output is correct
54	Correct	12 ms	12152 KB	Output is correct
55	Correct	12 ms	12024 KB	Output is correct
56	Correct	12 ms	12024 KB	Output is correct
57	Correct	13 ms	12152 KB	Output is correct
58	Correct	13 ms	12152 KB	Output is correct

Subtask #3
37.0 / 37.0

#	Verdict	Execution time	Memory	Grader output
1	Correct	13 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	12 ms	12152 KB	Output is correct
5	Correct	12 ms	12108 KB	Output is correct
6	Correct	12 ms	12024 KB	Output is correct
7	Correct	12 ms	12024 KB	Output is correct
8	Correct	14 ms	12028 KB	Output is correct
9	Correct	13 ms	12152 KB	Output is correct
10	Correct	12 ms	12024 KB	Output is correct
11	Correct	12 ms	12152 KB	Output is correct
12	Correct	13 ms	12152 KB	Output is correct
13	Correct	15 ms	12100 KB	Output is correct
14	Correct	16 ms	12152 KB	Output is correct
15	Correct	15 ms	12152 KB	Output is correct
16	Correct	12 ms	12024 KB	Output is correct
17	Correct	12 ms	12152 KB	Output is correct
18	Correct	12 ms	12152 KB	Output is correct
19	Correct	12 ms	12152 KB	Output is correct
20	Correct	13 ms	12152 KB	Output is correct
21	Correct	12 ms	12024 KB	Output is correct
22	Correct	13 ms	12280 KB	Output is correct
23	Correct	14 ms	12128 KB	Output is correct
24	Correct	16 ms	12152 KB	Output is correct
25	Correct	13 ms	12152 KB	Output is correct
26	Correct	13 ms	12152 KB	Output is correct
27	Correct	13 ms	12152 KB	Output is correct
28	Correct	16 ms	12124 KB	Output is correct
29	Correct	14 ms	12280 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	12152 KB	Output is correct
34	Correct	12 ms	12024 KB	Output is correct
35	Correct	12 ms	12152 KB	Output is correct
36	Correct	12 ms	12152 KB	Output is correct
37	Correct	12 ms	12156 KB	Output is correct
38	Correct	12 ms	12152 KB	Output is correct
39	Correct	12 ms	12024 KB	Output is correct
40	Correct	12 ms	12152 KB	Output is correct
41	Correct	12 ms	12024 KB	Output is correct
42	Correct	13 ms	12024 KB	Output is correct
43	Correct	13 ms	12168 KB	Output is correct
44	Correct	12 ms	12024 KB	Output is correct
45	Correct	12 ms	12024 KB	Output is correct
46	Correct	13 ms	12152 KB	Output is correct
47	Correct	12 ms	12152 KB	Output is correct
48	Correct	12 ms	12024 KB	Output is correct
49	Correct	13 ms	12152 KB	Output is correct
50	Correct	12 ms	12024 KB	Output is correct
51	Correct	12 ms	12024 KB	Output is correct
52	Correct	12 ms	12024 KB	Output is correct
53	Correct	12 ms	12152 KB	Output is correct
54	Correct	12 ms	12152 KB	Output is correct
55	Correct	12 ms	12024 KB	Output is correct
56	Correct	12 ms	12024 KB	Output is correct
57	Correct	13 ms	12152 KB	Output is correct
58	Correct	13 ms	12152 KB	Output is correct
59	Correct	390 ms	36112 KB	Output is correct
60	Correct	458 ms	38776 KB	Output is correct
61	Correct	12 ms	12024 KB	Output is correct
62	Correct	12 ms	12152 KB	Output is correct
63	Correct	366 ms	33740 KB	Output is correct
64	Correct	15 ms	12536 KB	Output is correct
65	Correct	27 ms	13944 KB	Output is correct
66	Correct	152 ms	27896 KB	Output is correct
67	Correct	527 ms	47024 KB	Output is correct
68	Correct	589 ms	47856 KB	Output is correct
69	Correct	20 ms	12920 KB	Output is correct
70	Correct	107 ms	21224 KB	Output is correct
71	Correct	382 ms	41912 KB	Output is correct
72	Correct	397 ms	40768 KB	Output is correct
73	Correct	129 ms	19064 KB	Output is correct
74	Correct	576 ms	37868 KB	Output is correct
75	Correct	47 ms	15352 KB	Output is correct
76	Correct	340 ms	41692 KB	Output is correct
77	Correct	335 ms	41808 KB	Output is correct
78	Correct	45 ms	15352 KB	Output is correct
79	Correct	525 ms	45276 KB	Output is correct
80	Correct	15 ms	12280 KB	Output is correct
81	Correct	123 ms	21332 KB	Output is correct
82	Correct	419 ms	39528 KB	Output is correct
83	Correct	470 ms	37736 KB	Output is correct
84	Correct	551 ms	37740 KB	Output is correct
85	Correct	491 ms	37708 KB	Output is correct
86	Correct	442 ms	38892 KB	Output is correct
87	Correct	519 ms	38816 KB	Output is correct

Submission #147130

Compilation message

Subtask #1 18.0 / 18.0

Subtask #2 45.0 / 45.0

Subtask #3 37.0 / 37.0

Subtask #1
18.0 / 18.0

Subtask #2
45.0 / 45.0

Subtask #3
37.0 / 37.0