/*input
*/
#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
#define double long double
#define f first
#define s second
#define mp make_pair
#define pb push_back
#define RE(i,n) for (int i = 1; i <= n; i++)
#define RED(i,n) for (int i = n; i > 0; i--)
#define REPS(i,n) for(int i = 1; (i*i) <= n; i++)
#define REP(i,n) for (int i = 0; i < (int)n; i++)
#define FOR(i,a,b) for (int i = a; i < b; i++)
#define REPD(i,n) for (int i = n-1; i >= 0; i--)
#define FORD(i,a,b) for (int i = a; i >= b; i--)
#define all(v) v.begin(),v.end()
#define pii pair<int,int>
#define vi vector<int>
#define vvi vector<vi>
#define print(arr) for (auto it = arr.begin(); it != arr.end(); ++it) cout << *it << " "; cout << endl;
#define debug(x) cout << x << endl;
#define debug2(x,y) cout << x << " " << y << endl;
#define debug3(x,y,z) cout << x << " " << y << " " << z << endl;
typedef tree<
int,
null_type,
less<int>,
rb_tree_tag,
tree_order_statistics_node_update>
ordered_set;
const int MOD = 1e9+7;
const double PI = 3.14159265358979323846264338;
int raise(int a,int n,int m = MOD){
if(n == 0)return 1;
if(n == 1)return a;
int x = 1;
x *= raise(a,n/2,m);
x %= m;
x *= x;
x %= m;
if(n%2)x*= a;
x %= m;
return x;
}
int floor1(int n,int k){
if(n%k == 0 || n >= 0)return n/k;
return (n/k)-1;
}
int ceil1(int n,int k){
return floor1(n+k-1,k);
}
const int N = 3e5+1;
int n,x,y;
vector<int> adj[N];
int vis = 0;
vector<pii> edges;
int par[N];
int F1,F2;
int trynow(int u,int p){
vector<int> childs;
for(int v:adj[u]){
if(v == p)continue;
if(min(u,v) == min(F1,F2) and max(u,v) == max(F1,F2))continue;
childs.pb(trynow(v,u));
}
sort(all(childs));reverse(all(childs));
int res = 0;
REP(i,childs.size()){
res = max(res,1+i+childs[i]);
}
return res;
}
void dfs0(int u,int p){
par[u] = p;
for(int v:adj[u]){
if(v == p)continue;
dfs0(v,u);
}
}
bool res(int i){
// deletes ith edge and tells which dp is greater
// 1 means x one is greater and 0 means other one
F1 = edges[i].f;
F2 = edges[i].s;
int one = trynow(x,0);
int two = trynow(y,0);
F1 = 0;F2 = 0;
return (one >= two);
}
int giveans(int i){
F1 = edges[i].f;
F2 = edges[i].s;
int one = trynow(x,0);
int two = trynow(y,0);
F1 = 0;F2 = 0;
return max(one,two);
}
void solve(){
cin >> n >> x >> y;
REP(i,n-1){
int a,b;
cin >> a >> b;
adj[a].pb(b);
adj[b].pb(a);
}
dfs0(x,0);
int u = y;
while(u != x){
edges.pb({par[u],u});
u = par[u];
}
reverse(all(edges));
// now as we keep deleting the edge which
// is further down dp of x will increase
// and dp of y will decrease
// we want first A such that sign_dp(A) and sign_dp(A+1) are opposit
if(res(0) or edges.size() == 1){
cout << giveans(0);
return;
}
int lo = 0;
int hi = edges.size();
hi -= 2;
while(lo <= hi){
int mid = (lo+hi)/2;
if(res(mid) != res(mid+1)){
//cout << mid << endl;
cout << min(giveans(mid),giveans(mid+1));
return;
}
else if(res(mid))hi = mid-1;
else lo = mid+1;
}
}
signed main(){
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
//freopen(".in","r",stdin);freopen(".out","w",stdout);
int t = 1;
//cin >> t;
while(t--){
solve();
}
return 0;
}
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
10 ms |
7416 KB |
Output is correct |
| 2 |
Correct |
9 ms |
7416 KB |
Output is correct |
| 3 |
Correct |
12 ms |
7416 KB |
Output is correct |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
1323 ms |
21700 KB |
Output is correct |
| 2 |
Correct |
1168 ms |
24024 KB |
Output is correct |
| 3 |
Correct |
1236 ms |
24032 KB |
Output is correct |
| 4 |
Correct |
1316 ms |
25904 KB |
Output is correct |
| 5 |
Correct |
358 ms |
21184 KB |
Output is correct |
| 6 |
Correct |
1249 ms |
21524 KB |
Output is correct |
| 7 |
Correct |
1184 ms |
25896 KB |
Output is correct |
