| # |
Submission time |
Handle |
Problem |
Language |
Result |
Execution time |
Memory |
| 301495 |
2020-09-18T03:04:35 Z |
eggag32 |
Network (BOI15_net) |
C++17 |
|
3 ms |
2688 KB |
#pragma GCC optimize ("O3")
#pragma GCC target ("sse4")
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef pair<int, int> pi;
#define debug(x) cerr << #x << ": " << x << endl
#define debug2(x, y) debug(x), debug(y)
#define repn(i, a, b) for(int i = (int)(a); i < (int)(b); i++)
#define rep(i, a) for(int i = 0; i < (int)(a); i++)
#define all(v) v.begin(), v.end()
#define mp make_pair
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define fi first
#define se second
#define sq(x) ((x) * (x))
const int mxN = 1e5 + 5;
template<class T> T gcd(T a, T b){ return ((b == 0) ? a : gcd(b, a % b)); }
vi g[mxN];
int ch[mxN], p[mxN], repr[mxN], vis[mxN], cnt1[mxN];
int mx = 0, bst = -1;
int mx1 = 0, bst1 = -1;
void dfs(int cur, int prev, int d){
if(d > mx){
mx = d;
bst = cur;
}
for(int x : g[cur]) if(x != prev) dfs(x, cur, d + 1);
}
void dfs1(int cur, int prev, int d){
if(d > mx1){
mx1 = d;
bst1 = cur;
}
p[cur] = prev;
for(int x : g[cur]) if(x != prev) dfs1(x, cur, d + 1);
}
vector<pi> fishyOrz;
void dfs2(int cur, int prev, int lst){
int cnt = 0;
if(ch[cur]) lst = cur;
for(int x : g[cur]) if(x != prev) dfs2(x, cur, lst), cnt++;
if(!cnt && !ch[cur]){
assert(lst != -1);
repr[lst] = cur;
cnt1[lst]++;
fishyOrz.pb({cur, lst});
}
}
bool cmp(pi a, pi b){
return a.se < b.se;
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
//freopen("input.in", "r", stdin);
//freopen("output.out", "w", stdout);
int n;
cin >> n;
rep(i, n - 1){
int a, b;
cin >> a >> b;
a--, b--;
g[a].pb(b);
g[b].pb(a);
}
dfs(0, -1, 0);
assert(bst != -1);
dfs1(bst, -1, 0);
assert(bst1 != -1);
int nw = bst1;
while(nw != -1){
ch[nw] = 1;
nw = p[nw];
}
dfs2(bst, -1, -1);
vector<pi> ans;
sort(all(fishyOrz), cmp);
int l = 0, r = (int)fishyOrz.size() - 1;
while(l <= r){
if(l == r){
int nd = -1;
for(int x : g[fishyOrz[l].se]) if(ch[x]) nd = x;
assert(nd != -1);
ans.pb({fishyOrz[l].fi, nd});
}
else{
ans.pb({fishyOrz[l].fi, fishyOrz[r].fi});
if(fishyOrz[l].se != fishyOrz[r].se){
vis[fishyOrz[l].se] = vis[fishyOrz[r].se] = 1;
}
}
l++, r--;
}
rep(i, n){
int nd = -1;
int nm1 = 0;
for(int x : g[i]) if(!ch[x]) nd = x, nm1++;
int nd1 = -1;
for(int x : g[i]) if(ch[x]) nd1 = x;
if(ch[i] && (nd != -1) && !vis[i] && (nd1 != -1) && cnt1[i] % 2 == 0 && nm1 == 1) ans.pb({repr[i], nd1});
}
ans.pb({bst, bst1});
cout << (int)ans.size() << '\n';
for(pi x : ans) cout << x.fi + 1 << " " << x.se + 1 << '\n';
return 0;
}
/*
Things to look out for:
- Integer overflows
- Array bounds
- Special cases
Be careful!
*/
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
3 ms |
2688 KB |
Output is correct |
| 2 |
Incorrect |
2 ms |
2688 KB |
Invalid number of links. |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
3 ms |
2688 KB |
Output is correct |
| 2 |
Incorrect |
2 ms |
2688 KB |
Invalid number of links. |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
3 ms |
2688 KB |
Output is correct |
| 2 |
Incorrect |
2 ms |
2688 KB |
Invalid number of links. |
| 3 |
Halted |
0 ms |
0 KB |
- |
