【模板】树的直径（树的最长路）

具体学习参考https://blog.csdn.net/qq_32400847/article/details/51469917

#include<queue>
#include<vector>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
struct Node
{
	int to,cap;
};
const int N=100010;
vector<Node> v[N];
int vis[N],dis[N],ans;

int bfs(int x)
{
    memset(dis,0,sizeof(dis));
    memset(vis,0,sizeof(vis));
    queue<int> q;
    q.push(x);
    vis[x]=1;
    int point=0;
    while(!q.empty())
    {
        int f=q.front();
        q.pop();
        if(dis[f]>ans)
        {
            ans=dis[f];
            point=f;
        }
        for(int i=0;i<v[f].size();i++)
        {
            Node temp=v[f][i];
            if(vis[temp.to]==0)
            {
                vis[temp.to]=1;
                dis[temp.to]=dis[f]+temp.cap;
                q.push(temp.to);
            }
        }
    }
    return point;
}

int main()
{
    int n;
    while(~scanf("%d",&n))
    {
        for(int i=1;i<=n-1;i++)
        {
            int x,y;
            scanf("%d %d",&x,&y);
            v[x].push_back((Node){y,1});
            v[y].push_back((Node){x,1});
        }
        ans=0;
        int point=bfs(1);
        ans=0;
        bfs(point);
        printf("%d\n",ans);
        for(int i=1;i<=n;i++) v[i].clear();
    }
}