luogu P1841 [JSOI2007]重要的城市 dp+Floyd

#include<map>
#include<queue>
#include<time.h>
#include<limits.h>
#include<cmath>
#include<ostream>
#include<iterator>
#include<set>
#include<stack>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
#define rep_1(i,m,n) for(int i=m;i<=n;i++)
#define mem(st) memset(st,0,sizeof st)
int read()
{
    int res=0,ch,flag=0;
    if((ch=getchar())=='-')             //判断正负
        flag=1;
    else if(ch>='0'&&ch<='9')           //得到完整的数
        res=ch-'0';
    while((ch=getchar())>='0'&&ch<='9')
        res=res*10+ch-'0';
    return flag?-res:res;
}
typedef long long ll;
typedef pair<int,int> pii;
typedef unsigned long long ull;
typedef pair<double,double> pdd;
const int inf = 0x3f3f3f3f;
const int N=210;
int dist[N][N];
int ans[N][N];
int n,m;
int res[N];
int main()
{
    cin>>n>>m;
    for(int i=1; i<=n; i++)
        for(int j=1; j<=n; j++)
            if(i!=j)
                dist[i][j]=dist[j][i]=2e6;
    for(int i=1; i<=m; i++)
    {
        int a,b,c;
        cin>>a>>b>>c;
        dist[a][b]=dist[b][a]=c;
    }
    for(int k=1; k<=n; k++)
        for(int i=1; i<=n; i++)
            if(i!=k)
                for(int j=1; j<=n; j++)
                    if(i!=j&&j!=k)
                    {
                        if(dist[i][j]>dist[i][k]+dist[k][j])
                            dist[i][j]=dist[i][k]+dist[k][j],ans[i][j]=k;
                        else if(dist[i][j]==dist[i][k]+dist[k][j])
                            ans[i][j]=-1;
                    }
    for(int i=1; i<=n; i++)
        for(int j=1; j<=n; j++)
            if(ans[i][j]!=-1)
                res[ans[i][j]]=1;
    int flag=0;
    for(int i=1; i<=n; i++)
        if(res[i]==1)
            cout<<i<<" ",flag=1;
    if(flag==0)
        cout<<"No important cities."<<endl;
    return 0;
}