Submission #507176

#	Time	Username	Problem	Language	Result	Execution time	Memory
507176		ponkung	Torrent (COI16_torrent)	C++14	0 / 100	176 ms	29148 KiB

torrent

#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 (stderr)

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);
      |         ~~~~~^~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 31
• Subtask 2: 0 / 69