spoj 1437

自己暴了一下不过     转一个 bfs...

#include <cstdio>

#include <vector>

#include <queue>

#include <cstring>

#define maxn 10010

using namespace std;

struct node

{

    int v,dist;

    node() {}

    node(int _v, int _dist)

    {

        v = _v;

        dist = _dist;

    }

} aux;

bool visited[maxn];

vector<int> L[maxn];

node search(int v)

{

    node ans = node(v,0);

    queue<node> Q;

    Q.push(node(v,0));

    memset(visited,false,sizeof(visited));

    visited[v] = true;

    while(!Q.empty())

    {

        aux = Q.front();

        Q.pop();

        ans = aux;

        for(int i = L[aux.v].size()-1; i >= 0; --i)

        {

            if(visited[L[aux.v][i]])

                continue;

            visited[L[aux.v][i]] = true;

            Q.push(node(L[aux.v][i], aux.dist+1));

        }

    }

    return ans;

}

int main()

{

    int N,u,v;

    scanf("%d",&N);

    for(int i = 1; i < N; ++i)

    {

        scanf("%d%d",&u,&v);

        L[u].push_back(v), L[v].push_back(u);

    }

    printf("%d\n",search(search(1).v).dist);

    return 0;

}