#include <bits/stdc++.h>
using namespace std;
#define all(x) x.begin() , x.end()
#define pii pair<int,int>
#define pll pair<ll,ll>
#define F first
#define S second
#define wall cerr<<"------------------------"<<endl
typedef long long ll;
const ll INF = 1e18;
const ll maxn = 1e6 + 10;
const ll mod = 1e9 + 7;
int n , m , k , ST , EN;
int h[maxn] , p[maxn] , st[maxn] , en[maxn];
int a[maxn<<1] , rmq[maxn<<1][21] , ps_rmq[maxn<<1][21] , rrmq[maxn<<1][21] , ps_rrmq[maxn<<1][21] , len[maxn<<1];
vector<int> g[maxn] , LSA;
bool mrk[maxn];
void DFS(int v)
{
mrk[v] = 1;
LSA.push_back(v);
st[v] = LSA.size()-1;
for(auto u : g[v]){
if(mrk[u]==1)continue;
p[u] = v;
h[u] = h[v]+1;
DFS(u);
LSA.push_back(v);
}
if(g[v].size()==1 && v!=1){
LSA.push_back(v);
}
en[v] = LSA.size()-1;
}
void pre_LCA()
{
LSA.push_back(0);
p[1] = -1;
DFS(1);
m = LSA.size()-1;
for(int i=1; i<=m; i++){
a[i] = h[LSA[i]];
}
for(int j=0; j<21; j++){
for(int i=1; i<=m; i++){
if(j==0){
rmq[i][j] = a[i];
rrmq[i][j] = a[i];
ps_rmq[i][j] = i;
ps_rrmq[i][j] = i;
continue;
}
if((i+(1<<j)-1)<=m){
rmq[i][j] = rmq[i][j-1];
ps_rmq[i][j] = ps_rmq[i][j-1];
if(rmq[i][j-1] > rmq[i+(1<<(j-1))][j-1]){
rmq[i][j] = rmq[i+(1<<(j-1))][j-1];
ps_rmq[i][j] = ps_rmq[i+(1<<(j-1))][j-1];
}
}
if((i-(1<<j)+1)>0){
rrmq[i][j] = rrmq[i][j-1];
ps_rrmq[i][j] = ps_rrmq[i][j-1];
if(rrmq[i][j-1] > rrmq[i-(1<<(j-1))][j-1]){
rrmq[i][j] = rrmq[i-(1<<(j-1))][j-1];
ps_rrmq[i][j] = ps_rrmq[i-(1<<(j-1))][j-1];
}
}
}
}
int PS = 0;
for(int i=1; i<=m; i++){
if(((1<<PS)<<1)<i){
PS++;
}
len[i] = PS;
}
}
int LCA(int v , int u)
{
int l = min(st[v],st[u]) , r=max(en[v],en[u]);
int ln = len[r-l+1];
int x = rmq[l][ln] , y = rrmq[r][ln];
if(x < y){
int pos = ps_rmq[l][ln];
return LSA[pos];
}else{
int pos = ps_rrmq[r][ln];
return LSA[pos];
}
}
int times=0;
map<int,bool> mp[maxn];
bool mark[maxn][30];
vector<int> ORDER;
vector<pii> eg[maxn];
int dfs(int v , int tm , int end)
{
//cout<<v<<"-->"<<end<<" : "<<tm<<"\n";
if(tm>25){
return -1;
}
if(v==end){
return 1;
}
mark[v][tm] = 1;
for(auto e : eg[v]){
int u=e.F , w=e.S;
int now = h[end]+h[v]-h[LCA(end,v)]-h[LCA(end,v)];
int then = h[end]+h[u]-h[LCA(end,u)]-h[LCA(end,u)];
if(then < now){
if(w==0){
dfs(u,tm,end);
}else{
if(mp[v][u]==0){
int tp = dfs(v,tm+1,w);
if(tp==-1){
return -1;
}
ORDER.push_back(w);
mp[v][u] = 1;
mp[u][v] = 1;
dfs(u,tm,end);
}else{
dfs(u,tm,end);
}
}
}
}
return 1;
}
int main()
{
ios_base::sync_with_stdio(0);cin.tie(NULL);cout.tie(NULL);
cin>>n>>ST>>EN;
for(int i=1; i<n; i++){
int v,u,w; cin>>v>>u>>w;
if(w==0){
mp[v][u] = 1;
mp[u][v] = 1;
}
eg[v].push_back({u,w});
eg[u].push_back({v,w});
g[v].push_back(u);
g[u].push_back(v);
}
pre_LCA();
ORDER.push_back(ST);
int tp = dfs(ST,1,EN);
ORDER.push_back(EN);
if(tp==-1){
cout<<"-1";
}else{
ll ans = 0 , sz=ORDER.size();
for(int i=1; i<sz; i++){
int v = ORDER[i-1] , u=ORDER[i];
ans += h[v]+h[u]-h[LCA(v,u)]-h[LCA(v,u)];
}
cout<<ans;
}
return 0;
}
/**
4
1 4
1 2 0
1 3 2
3 4 1
ans = 4;
*/
/*
5
3 1
1 2 5
2 3 4
3 4 0
4 5 2
ans = 10;
*/
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
42 ms |
94284 KB |
Output is correct |
| 2 |
Correct |
42 ms |
94224 KB |
Output is correct |
| 3 |
Correct |
232 ms |
201564 KB |
Output is correct |
| 4 |
Incorrect |
234 ms |
201672 KB |
Output isn't correct |
| 5 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
42 ms |
94328 KB |
Output is correct |
| 2 |
Correct |
42 ms |
94292 KB |
Output is correct |
| 3 |
Incorrect |
42 ms |
94440 KB |
Output isn't correct |
| 4 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
42 ms |
94284 KB |
Output is correct |
| 2 |
Correct |
42 ms |
94224 KB |
Output is correct |
| 3 |
Correct |
232 ms |
201564 KB |
Output is correct |
| 4 |
Incorrect |
234 ms |
201672 KB |
Output isn't correct |
| 5 |
Halted |
0 ms |
0 KB |
- |
