1167번_트리의 지름

문제 출처 : https://www.acmicpc.net/problem/1167

<C++Code>

#include<iostream>
#include<vector>
#include<queue>
#include<string.h>
#include<algorithm>
#define max 100001
using namespace std;
vector<pair<int,int> > a[max];
bool v[max];
queue<pair<int,int> > q;
int maxcnt=0;
int dist[max];
 
void  bfs(int start,int sum)
{
    memset(v,false,sizeof(v));
    memset(dist,0,sizeof(dist));
    q.push({start,0});
    v[start]=true;
    while(!q.empty())
    {
        int x=q.front().first;
        int cnt=q.front().second;
        q.pop();
        if(maxcnt<cnt)
        {
    
            maxcnt=cnt;
        
        }
        for(int i=0;i<a[x].size();i++)
        {
            int y=a[x][i].first;
            int nextcnt=a[x][i].second;
            if(!v[y])
            {
                dist[y]=nextcnt+cnt;
                v[y]=true;
                q.push({y,nextcnt+cnt});
            }
        }
    }
}
int main(void)
{
    
    int n;
    cin>>n;
for(int i=0;i<n;i++)
{
    int c;
    cin>>c;
    while(1)
    {
        int q;
        cin>>q;
        if(q==-1)
        {
         break;
        }
        int w;
        cin>>w;
        a[c].push_back({q,w});
    }
}
//vector<int> w;
    bfs(1,0);
    int start=1;
    for(int i=2;i<=n;i++)
    {
        if(dist[i]>dist[start])
        {
            start=i;
        }
    }
    //cout<<start<<endl;
    
    bfs(start,0);
    int ans=dist[1];
    for(int i=2;i<=n;i++)
    {
        if(dist[i]>ans)
        {
            ans=dist[i];
        }
    }
    cout<<ans<<endl;
    return 0;
    
    
}