Submission #474542

#	Time	Username	Problem	Language	Result	Execution time	Memory
474542		bin1st090104	Torrent (COI16_torrent)	C++11	100 / 100	416 ms	22940 KiB

torrent

#include <bits/stdc++.h>

using namespace std;

int const maxN=3e5;

int N,A,B;
vector<int> Adj[maxN+3];
int Cha[maxN+3],f[maxN+3];
int Tmp_array[maxN+3];
int Color[maxN+3];

void Dfs1(int u){
    for(int v:Adj[u]){
        if(v==Cha[u]){
            continue;
        }
        Cha[v]=u;
        Dfs1(v);
    }
    return ;
}

int Path[maxN+3];

void Dfs2(int u,int x,int p=-1){
    for(int v:Adj[u]){
        if(v==x||v==p){
            continue;
        }
        Dfs2(v,x,u);
    }
    int Cnt=0;
    for(int v:Adj[u]){
        if(v==x||v==p){
            continue;
        }
        Tmp_array[++Cnt]=f[v];
    }
    sort(Tmp_array+1,Tmp_array+Cnt+1,greater<int>());
    f[u]=0;
    for(int i=1;i<=Cnt;++i){
        f[u]=max(f[u],i+Tmp_array[i]);
    }
    return ;
}

int main(){
    cin.tie(nullptr)->sync_with_stdio(false);
    
    cin>>N>>A>>B;
    for(int i=1;i<N;++i){
        int u,v;
        cin>>u>>v;
        Adj[u].push_back(v);
        Adj[v].push_back(u);
    }
    Dfs1(A);
    int Len=0;
    {
        int u=B;
        do{
            Path[++Len]=u;
            if(u==A){
                break;
            }
            u=Cha[u];
        }
        while(1);
    }
    int l=1,r=Len-1,m,Res=1e9+7;
    while(l<=r){
        m=(l+r)>>1;
        Dfs2(A,Path[m]);
        Dfs2(B,Cha[Path[m]]);

        int x=f[B];
        int y=f[A];
        Res=min(Res,max(x,y));
        if(x<y){
            l=m+1;
        }
        else{
            r=m-1;
        }
    }
    cout<<Res;
    return 0;
}

• Subtask 1: 31 / 31
• Subtask 2: 69 / 69