Submission #507473

#	Time	Username	Problem	Language	Result	Execution time	Memory
507473		ToroTN	Torrent (COI16_torrent)	C++14	100 / 100	301 ms	24164 KiB

torrent

#include<bits/stdc++.h>
using namespace std;
int n,a,b,u_i,v_i,nxt[300005],u,it,m=0,st,md,ed,p[300005],dp[300005],mn=1e9,mx;
vector<int> v[300005],arr,g;
queue<int> q;
void dfs(int u,int fuck)
{
    if(v[u].size()==1&&v[u][0]==p[u]||u==fuck)
    {
        dp[u]=0;
        return;
    }
    for(int i=0;i<v[u].size();i++)
    {
        if(v[u][i]!=p[u])
        {
            p[v[u][i]]=u;
            dfs(v[u][i],fuck);
        }
    }
    for(int i=0;i<v[u].size();i++)
    {
        if(v[u][i]!=p[u]&&v[u][i]!=fuck)
        {
            g.push_back(dp[v[u][i]]);
        }
    }
    sort(g.begin(),g.end());
    for(int i=0;i<g.size();i++)
    {
        dp[u]=max(dp[u],g[i]+(int)g.size()-i);
    }
    g.clear();
}
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);
    }
    q.push(b);
    while(!q.empty())
    {
        u=q.front();
        q.pop();
        for(int i=0;i<v[u].size();i++)
        {
            if(nxt[v[u][i]]==0)
            {
                nxt[v[u][i]]=u;
                q.push(v[u][i]);
            }
        }
    }
    /*for(int i=1;i<=n;i++)
    {
        printf("%d=%d\n",i,nxt[i]);
    }*/
    arr.push_back(-1);
    it=a;
    while(1)
    {
        ++m;
        arr.push_back(it);
        if(it==b)
        {
            break;
        }
        it=nxt[it];
    }
    /*for(int i=1;i<=m;i++)
    {
        printf("%d ",arr[i]);
    }
    printf("\n");*/
    st=1;
    ed=m-1;
    while(ed>=st)
    {
        memset(dp,0,sizeof dp);
        md=(st+ed)/2;
        mx=-1;
        dfs(a,arr[md+1]);
        mx=max(mx,dp[a]);
        dfs(b,arr[md]);
        mx=max(mx,dp[b]);
        mn=min(mn,mx);
        //printf("%d %d %d %d %d %d %d\n",st,md,ed,arr[md],arr[md+1],dp[a],dp[b]);
        /*printf("%d %d %d %d %d\n",st,md,ed,dp[a],dp[b]);
        for(int i=1;i<=n;i++)
        {
            printf("%d %d\n",i,dp[i]);
        }*/
        if(dp[a]>=dp[b])
        {
            ed=md-1;
        }else
        {
            st=md+1;
        }
    }
    if(a==b)
    {
        dfs(a,0);
        printf("%d\n",dp[a]);
    }else
    {
        printf("%d\n",mn);
    }
}

Compilation message (stderr)

torrent.cpp: In function 'void dfs(int, int)':
torrent.cpp:8:22: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
    8 |     if(v[u].size()==1&&v[u][0]==p[u]||u==fuck)
      |        ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
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:21:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   21 |     for(int i=0;i<v[u].size();i++)
      |                 ~^~~~~~~~~~~~
torrent.cpp:29:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   29 |     for(int i=0;i<g.size();i++)
      |                 ~^~~~~~~~~
torrent.cpp: In function 'int main()':
torrent.cpp:49:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   49 |         for(int i=0;i<v[u].size();i++)
      |                     ~^~~~~~~~~~~~
torrent.cpp:37:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   37 |     scanf("%d%d%d",&n,&a,&b);
      |     ~~~~~^~~~~~~~~~~~~~~~~~~
torrent.cpp:40:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   40 |         scanf("%d%d",&u_i,&v_i);
      |         ~~~~~^~~~~~~~~~~~~~~~~~

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