#include <stdio.h>#include <string.h>#include <vector>#include <iostream>#include <string>#include <algorithm>using namespace std;bool map[10001][10001];int n;int tail;bool vis[1001];int fa[1001];void DFS_root(int dd){    int i, j;    for(i=1; i<=n; i++)    {        if(vis[i]==false && map[dd][i]==true )        {            fa[i]=fa[dd]+1;            vis[i]=true;            DFS_root(i);        }    }    int len=0;    tail=1;    for(j=2; j<=n; j++)    {        if(fa[j]>len)            tail=j;    }    //printf("%d***\n", tail );    return;}int len=0; //记录树中最长的路径长度void DFS_len_tree(int dd){    int i, j;    for(i=1; i<=n; i++)    {        if(vis[i]==false && map[dd][i]==true )        {            fa[i]=fa[dd]+1; //由前一个节点的长度+1过来的            vis[i]=true;            DFS_len_tree(i);        }    }    len=fa[1];    for(j=2; j<=n; j++)    {        if(fa[j]>len)            len=fa[j];    }}int main(){    int i, j;    int u, v;    scanf("%d", &n);    for(i=0; i<=n; i++ )    {        for(j=0; j<=n; j++)        {            map[i][j]=false;        }    } //map的初始化    for(i=0; i<n-1; i++)    {        scanf("%d %d", &u, &v );        map[u][v]=true;        map[v][u]=true;    }    memset(vis, false, sizeof(vis));    memset(fa, 0, sizeof(fa));    vis[1]=true;    DFS_root(1);    memset(vis, false, sizeof(vis));    memset(fa, 0, sizeof(fa)); //记录路径长度    vis[tail]=true;    DFS_len_tree(tail);    printf("%d\n", len );    return 0;}

#include <stdio.h>#include <string.h>#include <stdlib.h>#include <string>#include <iostream>#include <vector>#include <algorithm>#define N 100002using namespace std;vector<int>q[N];bool vis[N];int fa[N];int n, tail;int ans;void DFS_root(int dd){    int i, j;    int len;    len=q[dd].size();    for(i=0; i<len; i++)    {        if(vis[q[dd][i]]==false )        {            fa[q[dd][i]]=fa[dd]+1;            vis[q[dd][i]]=true;            DFS_root(q[dd][i]);        }    }    len=fa[1];tail=1;    for(j=2; j<=n; j++)    {        if(fa[j]>len)        {            len=fa[j];            tail=j;        }    }}void DFS_len_tree(int dd){    int len, i, j;    len=q[dd].size();    for(i=0; i<len; i++)    {        if(vis[q[dd][i]]==false)        {            fa[q[dd][i]]=fa[dd]+1;            vis[q[dd][i]]=true;            DFS_len_tree(q[dd][i]);        }    }}int main(){    int i, j;    int u, v;    scanf("%d", &n);    for(i=0; i<=n; i++)        q[i].clear();    for(i=0; i<n-1; i++)    {        scanf("%d %d", &u, &v);        q[u].push_back(v);        q[v].push_back(u);    }    memset(vis, false, sizeof(vis));    memset(fa, 0, sizeof(fa));    vis[1]=true;    DFS_root(1);    memset(vis, false, sizeof(vis));    memset(fa, 0, sizeof(fa));    vis[tail]=true;    DFS_len_tree(tail);    ans=fa[1];    for(j=2; j<=n; j++)    {        if(fa[j]>ans )            ans=fa[j];    }    printf("%d\n", ans );    return 0;}