#include<bits/stdc++.h>
#define DEBUG false
using namespace std;
int n, a, b;
vector<vector<int> > g;
vector<int> s;
vector<int> c;
bool dfs(int cur, int par){
s.push_back(cur);
if(cur == b){
return true;
}
for(int u: g[cur]){
if(u == par) continue;
if(dfs(u, cur)) return true;
}
s.pop_back();
return false;
}
int dfs2(int cur, int par){
vector<int> f;
for(int u: g[cur]){
if(c[u] || u == par) continue;
f.push_back(dfs2(u, cur));
}
sort(f.rbegin(), f.rend());
int ans = 0;
for(int i = 0; i < f.size(); i++){
ans = max(ans, f[i] + i+1);
}
return ans;
}
vector<vector<int> > h;
bool sim(int v){
if(DEBUG) cout<<"SIM "<<v<<endl;
int l1 = 0, l2 = 0;
int r1 = h.size()-1, r2 = 0;
bool pos = true;
int tym = 0;
while(l1 < r1){
if(l2 == h[l1].size() || h[l1][l2] + tym - (l2) + 1 <= v){
l1++; l2 = 0;
}else{
if(h[l1][l2] + tym - l2 > v){
return false;
}
l2++;
}
if(r2 == h[r1].size() || h[r1][r2] + tym - (r2) + 1 <= v){
r1--; r2 = 0;
}else{
if(h[r1][r2] + tym - r2 > v){
return false;
}
r2++;
}
tym++;
}
if(l2 == h[l1].size()) l1++;
if(r2 == h[r1].size()) r1--;
if(l1 == r1){
if(h[l1][max(l2, r2)] + tym - max(l2, r2) > v) return false;
}
return tym <= v;
}
signed main(){
cin>>n>>a>>b; a--, b--;
g.resize(n);
c.resize(n);
for(int i = 0; i < n-1; i++){
int x, y; cin>>x>>y; x--, y--;
g[x].push_back(y);
g[y].push_back(x);
}
dfs(a, -1);
for(int u: s){
c[u] = 1;
}
if(DEBUG)
for(int u: s){
cout<<" S: "<<u<<endl;
}
for(int u: s){
if(DEBUG) cout<<"DOING "<<u<<endl;
vector<int> k;
for(int d: g[u]){
if(c[d]) continue;
if(DEBUG) cout<<"DFS2 "<<d<<" "<<u<<endl;
k.push_back(dfs2(d, u));
}
sort(k.rbegin(), k.rend());
for(int i = 0; i < k.size(); i++) k[i] += i+1;
for(int i = k.size()-2; i >= 0; i--){
k[i] = max(k[i], k[i+1]);
}
h.push_back(k);
}
if(DEBUG)
for(vector<int> k: h){
for(int u: k){
cout<<u<<" ";
}
cout<<endl;
}
// cout<<"SIM 2: "<<sim(2)<<endl;
int low = 0, high = n, mid;
while(low < high){
mid = (low + high)/2;
//run it with ans mid and check if its possible
bool pos = sim(mid);
if(pos){
high = mid;
}else{
low = mid+1;
}
}
mid = (low + high)/2;
cout<<mid<<endl;
}
Compilation message
torrent.cpp: In function 'int dfs2(int, int)':
torrent.cpp:31:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
for(int i = 0; i < f.size(); i++){
~~^~~~~~~~~~
torrent.cpp: In function 'bool sim(int)':
torrent.cpp:47:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
if(l2 == h[l1].size() || h[l1][l2] + tym - (l2) + 1 <= v){
~~~^~~~~~~~~~~~~~~
torrent.cpp:57:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
if(r2 == h[r1].size() || h[r1][r2] + tym - (r2) + 1 <= v){
~~~^~~~~~~~~~~~~~~
torrent.cpp:67:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
if(l2 == h[l1].size()) l1++;
~~~^~~~~~~~~~~~~~~
torrent.cpp:68:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
if(r2 == h[r1].size()) r1--;
~~~^~~~~~~~~~~~~~~
torrent.cpp:44:7: warning: unused variable 'pos' [-Wunused-variable]
bool pos = true;
^~~
torrent.cpp: In function 'int main()':
torrent.cpp:104:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
for(int i = 0; i < k.size(); i++) k[i] += i+1;
~~^~~~~~~~~~
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
3 ms |
632 KB |
Output is correct |
| 2 |
Correct |
3 ms |
376 KB |
Output is correct |
| 3 |
Correct |
3 ms |
376 KB |
Output is correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
446 ms |
25116 KB |
Output is correct |
| 2 |
Correct |
425 ms |
26420 KB |
Output is correct |
| 3 |
Correct |
418 ms |
27620 KB |
Output is correct |
| 4 |
Correct |
416 ms |
27752 KB |
Output is correct |
| 5 |
Correct |
424 ms |
24508 KB |
Output is correct |
| 6 |
Correct |
412 ms |
24704 KB |
Output is correct |
| 7 |
Correct |
417 ms |
28040 KB |
Output is correct |
