csu

http://acm.csu.edu.cn/OnlineJudge/problem.php?id=1659

题意是找一个图的中心,图的中心定义是某一个点到其他点的最大距离最小,如果有多个排序输出.

注意这里大到其他点的距离是找一个最短的距离,那么就转化成了最短路的问题,求出每个点与其它点的最大距离,

保存并且求出最大距离中的最小距离,然后判断有几个点满足条件输出即可.

#include <iostream>
#include <cstdio>
#include <cmath>
#include <vector>
#include <cstring>
#include <string>
#include <algorithm>
#include <string>
#include <set>
#include <functional>
#include <numeric>
#include <sstream>
#include <stack>
#include <map>
#include <queue>
#include <deque>
//#pragma comment(linker, "/STACK:102400000,102400000")
#define CL(arr, val)    memset(arr, val, sizeof(arr))

#define ll long long
#define INF 0x7f7f7f7f
#define lc l,m,rt<<1
#define rc m + 1,r,rt<<1|1
#define pi acos(-1.0)

#define L(x)    (x) << 1
#define R(x)    (x) << 1 | 1
#define MID(l, r)   (l + r) >> 1
#define Min(x, y)   (x) < (y) ? (x) : (y)
#define Max(x, y)   (x) < (y) ? (y) : (x)
#define E(x)        (1 << (x))
#define iabs(x)     (x) < 0 ? -(x) : (x)
#define OUT(x)  printf("%I64d
", x)
#define lowbit(x)   (x)&(-x)
#define Read()  freopen("a.txt", "r", stdin)
#define Write() freopen("b.txt", "w", stdout);
#define maxn 110
#define maxv 5010
#define mod 1000000000
using namespace std;

struct edge
{
    int to,weight;
    edge() {}
    edge(int a,int b)
    {
        to=a;
        weight=b;
    }
};

vector<edge>adjmap[maxv];
bool in_queue[maxn];
int dist[maxn];
int n,m,p[maxn],ans[maxn];

int spfa(int a)
{
    queue<int>que;
    for(int i=1;i<=n;i++)
    {
        in_queue[i]=false;
        dist[i]=INF;
    }
    que.push(a);
    dist[a]=0;
    in_queue[a]=true;
    while(!que.empty())
    {
        int x=que.front();que.pop();
        in_queue[x]=false;
        for(int i=0;i<adjmap[x].size();i++)
        {
            int to=adjmap[x][i].to;
            edge temp=adjmap[x][i];
            if(dist[x]<INF&&(dist[to]>dist[x]+temp.weight))
            {
                if(!in_queue[to])
                {
                    in_queue[to]=true;
                    dist[to]=dist[x]+temp.weight;
                    que.push(to);
                }
            }
        }
    }
    int x=0;
    for(int i=1;i<=n;i++)
        x=max(x,dist[i]);
    return x;
}
int main()
{
    //Read();
    int t,a,b;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d%d",&n,&m);
        for(int i=1;i<=n;i++) adjmap[i].clear();
        for(int i=1;i<=m;i++)
        {
            scanf("%d%d",&a,&b);
            adjmap[a].push_back(edge(b,1));
            adjmap[b].push_back(edge(a,1));
        }
        int x=INF,j=0;
        for(int i=1;i<=n;i++)
        {
            p[i]=spfa(i);
            x=min(x,p[i]);
        }
        for(int i=1;i<=n;i++)
        {
            if(p[i]==x) ans[j++]=i;
        }
        printf("%d
",j);
        for(int i=0;i<j;i++)
        {
            if(i!=j-1) printf("%d ",ans[i]);
            else printf("%d
",ans[i]);
        }
    }
    return 0;
}