//LaziChicken - 9/2023
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ld long double
#define pii pair <int, int>
#define pll pair <ll, ll>
#define pli pair <ll, int>
#define pil pair <int, ll>
#define fi first
#define se second
#define dim 3
#define tii tuple <int, int, int>
#define inf 0x3f
const ll nx = 3e5+2;
const ll bx = 1e3+2;
const ll mod = 1e9+7;
//--------------------------------
int n, a, b, pre[nx];
int res = 1e9, dist[2][nx];
vector <int> adj[nx], trace;
void dfstrace(int par, int u){
for (auto v : adj[u]){
if (v == par) continue;
pre[v] = u;
dfstrace(u, v);
}
}
int dfs(bool dir, int par, int u, int ban){
vector <int> vt;
for (auto v : adj[u]){
if (v == par or v == ban) continue;
vt.emplace_back(dfs(dir, u, v, ban));
}
sort(vt.begin(), vt.end(), greater<int>());
for (int i = 0; i < vt.size(); i++){
dist[dir][u] = max(dist[dir][u], vt[i] + i + 1);
}
return dist[dir][u];
}
bool check(int mid){
memset(dist, 0, sizeof(dist));
dfs(0, 0, a, trace[mid+1]);
dfs(1, 0, b, trace[mid]);
res = min(res, max(dist[0][a], dist[1][b]));
return dist[0][a] < dist[1][b];
}
void bs(int l, int r){
while(l <= r){
int mid = (l + r) >> 1;
if (check(mid)) l = mid + 1;
else r = mid - 1;
}
}
//--------------------------------
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
cin >> n >> a >> b;
for (int i = 1, u, v; i < n; i++){
cin >> u >> v;
adj[u].emplace_back(v);
adj[v].emplace_back(u);
}
dfstrace(0, a);
int tmp = b; trace.emplace_back(b);
while(tmp != a){
if (tmp != b and tmp != a) trace.emplace_back(tmp);
tmp = pre[tmp];
}
trace.emplace_back(a);
reverse(trace.begin(), trace.end());
bs(0, trace.size() - 2);
cout << res;
}
/*
Note:
*/
Compilation message
torrent.cpp: In function 'int dfs(bool, int, int, int)':
torrent.cpp:43:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
43 | for (int i = 0; i < vt.size(); i++){
| ~~^~~~~~~~~~~
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
4 ms |
10840 KB |
Output is correct |
2 |
Correct |
4 ms |
10848 KB |
Output is correct |
3 |
Correct |
3 ms |
10840 KB |
Output is correct |
# |
Verdict |
Execution time |
Memory |
Grader output |
1 |
Correct |
270 ms |
23024 KB |
Output is correct |
2 |
Correct |
306 ms |
24372 KB |
Output is correct |
3 |
Correct |
264 ms |
26192 KB |
Output is correct |
4 |
Correct |
293 ms |
25572 KB |
Output is correct |
5 |
Correct |
277 ms |
22352 KB |
Output is correct |
6 |
Correct |
257 ms |
23040 KB |
Output is correct |
7 |
Correct |
298 ms |
26520 KB |
Output is correct |