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.

  1 #include <iostream>
  2 #include <cstdio>
  3 #include <cmath>
  4 #include <vector>
  5 #include <cstring>
  6 #include <string>
  7 #include <algorithm>
  8 #include <string>
  9 #include <set>
 10 #include <functional>
 11 #include <numeric>
 12 #include <sstream>
 13 #include <stack>
 14 #include <map>
 15 #include <queue>
 16 #include <deque>
 17 //#pragma comment(linker, "/STACK:102400000,102400000")
 18 #define CL(arr, val)    memset(arr, val, sizeof(arr))
 19 
 20 #define ll long long
 21 #define INF 0x7f7f7f7f
 22 #define lc l,m,rt<<1
 23 #define rc m + 1,r,rt<<1|1
 24 #define pi acos(-1.0)
 25 
 26 #define L(x)    (x) << 1
 27 #define R(x)    (x) << 1 | 1
 28 #define MID(l, r)   (l + r) >> 1
 29 #define Min(x, y)   (x) < (y) ? (x) : (y)
 30 #define Max(x, y)   (x) < (y) ? (y) : (x)
 31 #define E(x)        (1 << (x))
 32 #define iabs(x)     (x) < 0 ? -(x) : (x)
 33 #define OUT(x)  printf("%I64d
", x)
 34 #define lowbit(x)   (x)&(-x)
 35 #define Read()  freopen("a.txt", "r", stdin)
 36 #define Write() freopen("b.txt", "w", stdout);
 37 #define maxn 110
 38 #define maxv 5010
 39 #define mod 1000000000
 40 using namespace std;
 41 
 42 struct edge
 43 {
 44     int to,weight;
 45     edge() {}
 46     edge(int a,int b)
 47     {
 48         to=a;
 49         weight=b;
 50     }
 51 };
 52 
 53 vector<edge>adjmap[maxv];
 54 bool in_queue[maxn];
 55 int dist[maxn];
 56 int n,m,p[maxn],ans[maxn];
 57 
 58 int spfa(int a)
 59 {
 60     queue<int>que;
 61     for(int i=1;i<=n;i++)
 62     {
 63         in_queue[i]=false;
 64         dist[i]=INF;
 65     }
 66     que.push(a);
 67     dist[a]=0;
 68     in_queue[a]=true;
 69     while(!que.empty())
 70     {
 71         int x=que.front();que.pop();
 72         in_queue[x]=false;
 73         for(int i=0;i<adjmap[x].size();i++)
 74         {
 75             int to=adjmap[x][i].to;
 76             edge temp=adjmap[x][i];
 77             if(dist[x]<INF&&(dist[to]>dist[x]+temp.weight))
 78             {
 79                 if(!in_queue[to])
 80                 {
 81                     in_queue[to]=true;
 82                     dist[to]=dist[x]+temp.weight;
 83                     que.push(to);
 84                 }
 85             }
 86         }
 87     }
 88     int x=0;
 89     for(int i=1;i<=n;i++)
 90         x=max(x,dist[i]);
 91     return x;
 92 }
 93 int main()
 94 {
 95     //Read();
 96     int t,a,b;
 97     scanf("%d",&t);
 98     while(t--)
 99     {
100         scanf("%d%d",&n,&m);
101         for(int i=1;i<=n;i++) adjmap[i].clear();
102         for(int i=1;i<=m;i++)
103         {
104             scanf("%d%d",&a,&b);
105             adjmap[a].push_back(edge(b,1));
106             adjmap[b].push_back(edge(a,1));
107         }
108         int x=INF,j=0;
109         for(int i=1;i<=n;i++)
110         {
111             p[i]=spfa(i);
112             x=min(x,p[i]);
113         }
114         for(int i=1;i<=n;i++)
115         {
116             if(p[i]==x) ans[j++]=i;
117         }
118         printf("%d
",j);
119         for(int i=0;i<j;i++)
120         {
121             if(i!=j-1) printf("%d ",ans[i]);
122             else printf("%d
",ans[i]);
123         }
124     }
125     return 0;
126 }