#include "bits/stdc++.h"
using namespace std;
int deg[500010];
deque <int> nodes;
vector <int> g[500010];
int sub[500010];
int parent[500010];
void leaf(int x, int par) {
if(deg[x] == 1) sub[x] = 1;
else sub[x] = 0;
for(auto i : g[x]) {
if(i - par) {
leaf(i, x);
sub[x] += sub[i];
}
}
}
int centroid(int x, int par, int range) {
for(auto i : g[x]) {
if(i - par) {
if(sub[i] > range) {
return centroid(i, x, range);
}
}
}
return x;
}
void dfs(int x, int par) {
parent[x] = par;
if(deg[x] == 1) {
nodes.push_back(x);
}
for(auto i : g[x]) {
if(i - par) {
dfs(i, x);
}
}
}
bool vis[500010];
int lca(int x, int y) {
memset(vis, false, sizeof vis);
while(x != 0) {
vis[x] = true;
x = parent[x];
}
while(y != 0) {
if(vis[y] == true) return y;
y = parent[y];
}
return 1;
}
int main(int argc, char const *argv[])
{
int n;
scanf("%d", &n);
for(int i = 1; i < n; i++) {
int p, q;
scanf("%d %d", &p, &q);
++deg[p];
++deg[q];
g[p].push_back(q);
g[q].push_back(p);
}
int root = 0;
for(int i = 1; i <= n; i++) {
if(deg[i] != 1) {
root = i;
break;
}
}
leaf(root, 0);
int half = (sub[root] + 1) >> 1;
int leave = sub[root];
int centre = centroid(root, 0, half);
dfs(centre, 0);
leaf(centre, 0);
assert(deg[centre] != 1);
for(auto i : g[centre]) {
if(sub[i] > half) {
assert(false);
}
}
printf("%d\n", half);
for(int i = 0; i + half < leave; i++) {
printf("%d %d\n", nodes[i], nodes[i + half]);
}
if(leave & 1) {
if(lca(nodes[half-1], nodes.back()) == centre) printf("%d %d\n", nodes[half-1], nodes.back());
else printf("%d %d\n", nodes[half-1], nodes.front());
}
return 0;
}
Compilation message
net.cpp: In function 'int main(int, const char**)':
net.cpp:61:17: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
scanf("%d", &n);
^
net.cpp:65:25: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
scanf("%d %d", &p, &q);
^
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 2 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 3 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 4 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 5 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 6 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 7 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 8 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 9 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 10 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 11 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 12 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 13 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 14 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 15 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 16 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 17 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 18 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 19 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 20 |
Correct |
3 ms |
20088 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 2 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 3 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 4 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 5 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 6 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 7 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 8 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 9 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 10 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 11 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 12 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 13 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 14 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 15 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 16 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 17 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 18 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 19 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 20 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 21 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 22 |
Correct |
0 ms |
20220 KB |
Output is correct |
| 23 |
Correct |
3 ms |
20220 KB |
Output is correct |
| 24 |
Correct |
3 ms |
20220 KB |
Output is correct |
| 25 |
Correct |
0 ms |
20220 KB |
Output is correct |
| 26 |
Correct |
3 ms |
20220 KB |
Output is correct |
| 27 |
Correct |
3 ms |
20220 KB |
Output is correct |
| 28 |
Correct |
0 ms |
20220 KB |
Output is correct |
| 29 |
Correct |
3 ms |
20220 KB |
Output is correct |
| 30 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 31 |
Correct |
6 ms |
20220 KB |
Output is correct |
| 32 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 33 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 34 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 35 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 36 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 37 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 38 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 39 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 40 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 41 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 42 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 43 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 44 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 45 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 46 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 47 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 48 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 49 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 50 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 51 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 52 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 53 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 54 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 55 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 56 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 57 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 58 |
Correct |
3 ms |
20220 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 2 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 3 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 4 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 5 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 6 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 7 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 8 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 9 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 10 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 11 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 12 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 13 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 14 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 15 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 16 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 17 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 18 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 19 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 20 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 21 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 22 |
Correct |
0 ms |
20220 KB |
Output is correct |
| 23 |
Correct |
3 ms |
20220 KB |
Output is correct |
| 24 |
Correct |
3 ms |
20220 KB |
Output is correct |
| 25 |
Correct |
0 ms |
20220 KB |
Output is correct |
| 26 |
Correct |
3 ms |
20220 KB |
Output is correct |
| 27 |
Correct |
3 ms |
20220 KB |
Output is correct |
| 28 |
Correct |
0 ms |
20220 KB |
Output is correct |
| 29 |
Correct |
3 ms |
20220 KB |
Output is correct |
| 30 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 31 |
Correct |
6 ms |
20220 KB |
Output is correct |
| 32 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 33 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 34 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 35 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 36 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 37 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 38 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 39 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 40 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 41 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 42 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 43 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 44 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 45 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 46 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 47 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 48 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 49 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 50 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 51 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 52 |
Correct |
6 ms |
20088 KB |
Output is correct |
| 53 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 54 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 55 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 56 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 57 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 58 |
Correct |
3 ms |
20220 KB |
Output is correct |
| 59 |
Correct |
729 ms |
36460 KB |
Output is correct |
| 60 |
Correct |
829 ms |
37784 KB |
Output is correct |
| 61 |
Correct |
0 ms |
20088 KB |
Output is correct |
| 62 |
Correct |
3 ms |
20088 KB |
Output is correct |
| 63 |
Correct |
619 ms |
34344 KB |
Output is correct |
| 64 |
Correct |
6 ms |
20400 KB |
Output is correct |
| 65 |
Correct |
26 ms |
21884 KB |
Output is correct |
| 66 |
Correct |
309 ms |
36260 KB |
Output is correct |
| 67 |
Correct |
1116 ms |
52292 KB |
Output is correct |
| 68 |
Correct |
1096 ms |
52880 KB |
Output is correct |
| 69 |
Correct |
13 ms |
20656 KB |
Output is correct |
| 70 |
Correct |
129 ms |
26684 KB |
Output is correct |
| 71 |
Correct |
589 ms |
39860 KB |
Output is correct |
| 72 |
Correct |
603 ms |
39724 KB |
Output is correct |
| 73 |
Correct |
169 ms |
24840 KB |
Output is correct |
| 74 |
Correct |
899 ms |
37280 KB |
Output is correct |
| 75 |
Correct |
43 ms |
22260 KB |
Output is correct |
| 76 |
Correct |
556 ms |
39736 KB |
Output is correct |
| 77 |
Correct |
603 ms |
39900 KB |
Output is correct |
| 78 |
Correct |
86 ms |
23076 KB |
Output is correct |
| 79 |
Correct |
1022 ms |
49972 KB |
Output is correct |
| 80 |
Correct |
6 ms |
20220 KB |
Output is correct |
| 81 |
Correct |
209 ms |
26556 KB |
Output is correct |
| 82 |
Correct |
776 ms |
38560 KB |
Output is correct |
| 83 |
Correct |
926 ms |
37280 KB |
Output is correct |
| 84 |
Correct |
889 ms |
37284 KB |
Output is correct |
| 85 |
Correct |
933 ms |
37280 KB |
Output is correct |
| 86 |
Correct |
883 ms |
37788 KB |
Output is correct |
| 87 |
Correct |
886 ms |
37788 KB |
Output is correct |
