#include <bits/stdc++.h>
//#define double double
#define int long long
#define rep(i,n) for(int i = 0; i < n; i++)
#define all(a) a.begin(), a.end()
using namespace std;
vector<vector<int>>E;
int t,m;
int dfs(int v, int p)
{
priority_queue<int>pq;
int children = 0;
for(int w : E[v])
{
if(w==p||w==t) continue;
children++;
pq.push(-dfs(w,v));
if(pq.size()>2) pq.pop();
}
int sum = min((int)1, children); //block biggest child
if(children>1)
{
sum-=pq.top()-1; // cost of second biggest child + cleaning
sum+=children-2; // block children 3 .. children
}
return sum;
}
vector<int>path;
vector<int>par;
void find_path(int v)
{
if(v==m)
{
while (v!=t)
{
path.push_back(v);
v = par[v];
}
return;
}
for(int w : E[v])
{
if(w==par[v]) continue;
par[w]=v;
find_path(w);
}
}
vector<int>f;
int get(int k)
{
k++;
int sum =0;
for(int i = k; i>0;i-=i&-1) sum+=f[i];
return sum;
}
void update(int k)
{
k++;
for(int i = k; i<f.size(); i+=i&-i) f[i]++;
}
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
int n;
cin>>n>>t>>m;
t--;
m--;
if(t==m)
{
cout<<0<<"\n";
exit(0);
}
E.resize(n);
par.assign(n, -1);
rep(i, n-1)
{
int a,b;
cin>>a>>b;
a--;b--;
E[a].push_back(b);
E[b].push_back(a);
}
find_path(t);
//path from mouse to trap;
vector<int>suff(path.size());
for(int i = path.size()-1; i>=0; i--)
{
suff[i] = E[path[i]].size()-1;
if(i<path.size()-1) suff[i]+=suff[i+1]-1;
}
vector<pair<int, int>>costs;
rep(i, path.size())
{
int v = path[i];
for(int w : E[v])
{
if((i>0&&w==path[i-1]||(i+1<path.size()&&w==path[i+1]))||w==t) continue;
int c = dfs(w, v) + suff[i]; // suff because all except that edge need to be blocked and that edge needs to be cleaned
costs.push_back({c, i});
}
}
sort(all(costs));
reverse(all(costs));
int maxx = 0;
f.assign(n+1, 0);
for(auto cost : costs)
{
if(get(cost.second)<cost.second+1) maxx=max(maxx, cost.first);
else update(cost.second);
}
cout<<maxx<<"\n";
}
Compilation message
mousetrap.cpp: In function 'void update(long long int)':
mousetrap.cpp:67:21: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
67 | for(int i = k; i<f.size(); i+=i&-i) f[i]++;
| ~^~~~~~~~~
mousetrap.cpp: In function 'int main()':
mousetrap.cpp:101:13: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
101 | if(i<path.size()-1) suff[i]+=suff[i+1]-1;
| ~^~~~~~~~~~~~~~
mousetrap.cpp:4:35: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
4 | #define rep(i,n) for(int i = 0; i < n; i++)
......
105 | rep(i, path.size())
| ~~~~~~~~~~~~~~
mousetrap.cpp:105:5: note: in expansion of macro 'rep'
105 | rep(i, path.size())
| ^~~
mousetrap.cpp:110:40: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
110 | if((i>0&&w==path[i-1]||(i+1<path.size()&&w==path[i+1]))||w==t) continue;
| ~~~^~~~~~~~~~~~
mousetrap.cpp:110:20: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
110 | if((i>0&&w==path[i-1]||(i+1<path.size()&&w==path[i+1]))||w==t) continue;
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
0 ms |
204 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
424 ms |
78544 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
0 ms |
204 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
0 ms |
204 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
