#include<bits/stdc++.h>
using namespace std;
int n,a,b,u_i,v_i,dp[300005],p[300005],lv[300005],ans=-1,mx,it,hsh[300005],dis1[300005],dis2[300005],u;
vector<int> v[300005],g;
queue<int> q;
void dfs(int u)
{
if(v[u].size()==1&&v[u][0]==p[u])
{
//printf("node=%d\n",u);
return;
}
for(int i=0;i<v[u].size();i++)
{
if(p[u]!=v[u][i])
{
lv[v[u][i]]=lv[u]+1;
p[v[u][i]]=u;
dfs(v[u][i]);
}
}
for(int i=0;i<v[u].size();i++)
{
if(v[u][i]!=p[u])
{
g.push_back(dp[v[u][i]]);
}
}
//printf("node=%d\n",u);
sort(g.begin(),g.end());
for(int i=0;i<g.size();i++)
{
dp[u]=max(dp[u],g[i]+(int)g.size()-i);
//printf("%d ",g[i]);
}
//printf("\n");
g.clear();
}
int lca(int x,int y)
{
while(1)
{
//printf("%d %d %d %d\n",x,y,lv[x],lv[y]);
if(lv[x]==lv[y])
{
if(x==y)
{
return x;
}else
{
x=p[x];
}
}else if(lv[x]>=lv[y])
{
x=p[x];
}else
{
y=p[y];
}
}
}
int compute(int x,int y)
{
mx=-1;
it=0;
while(1)
{
//printf("node=%d\n",x);
//printf("it=%d\n",it);
mx=max(mx,it);
for(int i=0;i<v[x].size();i++)
{
if(v[x][i]!=p[x]&&hsh[v[x][i]]==0)
{
g.push_back(dp[v[x][i]]);
}
}
sort(g.begin(),g.end());
for(int i=0;i<g.size();i++)
{
mx=max(mx,it+g[i]+(int)g.size()-i);
//printf("%d ",g[i]);
}
//printf("\n");
//printf("max=%d\n",mx);
g.clear();
if(x==y)
{
break;
}
hsh[x]=1;
x=p[x];
it=min(dis1[x],dis2[x]);
}
return mx;
}
int main()
{
scanf("%d%d%d",&n,&a,&b);
for(int i=1;i<n;i++)
{
scanf("%d%d",&u_i,&v_i);
v[u_i].push_back(v_i);
v[v_i].push_back(u_i);
}
dfs(1);
/*for(int i=1;i<=n;i++)
{
printf("%d\n",dp[i]);
}*/
/*for(int i=1;i<=n;i++)
{
printf("%d\n",lv[i]);
}*/
memset(dis1,-1,sizeof dis1);
memset(dis2,-1,sizeof dis2);
dis1[a]=0;
dis2[b]=0;
q.push(a);
while(!q.empty())
{
u=q.front();
q.pop();
for(int i=0;i<v[u].size();i++)
{
if(dis1[v[u][i]]==-1)
{
dis1[v[u][i]]=dis1[u]+1;
q.push(v[u][i]);
}
}
}
q.push(b);
while(!q.empty())
{
u=q.front();
q.pop();
for(int i=0;i<v[u].size();i++)
{
if(dis2[v[u][i]]==-1)
{
dis2[v[u][i]]=dis2[u]+1;
q.push(v[u][i]);
}
}
}
/*for(int i=1;i<=n;i++)
{
printf("%d %d\n",dis1[i],dis2[i]);
}*/
ans=max(ans,compute(a,lca(a,b)));
ans=max(ans,compute(b,lca(a,b)));
ans=max(ans,compute(lca(a,b),1));
printf("%d\n",ans);
}
Compilation message
torrent.cpp: In function 'void dfs(int)':
torrent.cpp:13:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
13 | for(int i=0;i<v[u].size();i++)
| ~^~~~~~~~~~~~
torrent.cpp:22:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
22 | for(int i=0;i<v[u].size();i++)
| ~^~~~~~~~~~~~
torrent.cpp:31:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
31 | for(int i=0;i<g.size();i++)
| ~^~~~~~~~~
torrent.cpp: In function 'int compute(int, int)':
torrent.cpp:71:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
71 | for(int i=0;i<v[x].size();i++)
| ~^~~~~~~~~~~~
torrent.cpp:79:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
79 | for(int i=0;i<g.size();i++)
| ~^~~~~~~~~
torrent.cpp: In function 'int main()':
torrent.cpp:124:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
124 | for(int i=0;i<v[u].size();i++)
| ~^~~~~~~~~~~~
torrent.cpp:138:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
138 | for(int i=0;i<v[u].size();i++)
| ~^~~~~~~~~~~~
torrent.cpp:99:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
99 | scanf("%d%d%d",&n,&a,&b);
| ~~~~~^~~~~~~~~~~~~~~~~~~
torrent.cpp:102:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
102 | scanf("%d%d",&u_i,&v_i);
| ~~~~~^~~~~~~~~~~~~~~~~~
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
6 ms |
9676 KB |
Output is correct |
| 2 |
Incorrect |
5 ms |
9716 KB |
Output isn't correct |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Incorrect |
176 ms |
29148 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
