hihoCoder 1050 树中的最长路

#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>
using namespace std;

vector<int> v[100005];
int n;
int vis[100005];
int dis[100005];

int dfs(int x,int d){
    vis[x] = 1;
    dis[x] = d;
    for(int i = 0; i < v[x].size(); i++){
        if(!vis[v[x][i]]){
            dfs(v[x][i],d+1);
        }
    }
}

int main(){
    while(scanf("%d",&n) != EOF){
        int x,y;
        for(int i = 1; i < n; i++){
            scanf("%d%d",&x,&y);
            v[x].push_back(y);
            v[y].push_back(x);
        }
        memset(vis,0,sizeof(vis));
        dfs(1,0);
        int ans = 0,tmp;
        for(int i = 1; i <= n; i++){
            if(ans < dis[i]){
                ans = dis[i];
                tmp = i;
            }
        }
        memset(vis,0,sizeof(vis));
        dfs(tmp,0);
        for(int i = 1; i <= n; i++){
            if(ans < dis[i])
                ans = dis[i];
        }
        printf("%d\n",ans);
    }
    return 0;
}