最小環模板

floyed

http://acm.hdu.edu.cn/showproblem.php?pid=1599

#include <bits/stdc++.h>
#define inf 2333333333333
#define N 210
#define p(a) putchar(a)
#define For(i,a,b) for(long long i=a;i<=b;++i)
//by war
//2020.8.4
using namespace std;
long long n,m,x,y,v,ans;
long long f[N][N],val[N][N];
void in(long
 
 long &x){
    long long y=1;char c=getchar();x=0;
    while(c<'0'||c>'9'){if(c=='-')y=-1;c=getchar();}
    while(c<='9'&&c>='0'){ x=(x<<1)+(x<<3)+c-'0';c=getchar();}
    x*=y;
}
void o(long long x){
    if(x<0){p('-');x=-x;}
    if(x>9)o(x/10);
    p(x%10+'0');
}

signed main(){
    
 
while(cin>>n>>m){
        ans=inf;
        For(i,1,n)
            For(j,1,n)
                f[i][j]=val[i][j]=inf;
        For(i,1,m){
            in(x);in(y);in(v);
            if(v<f[x][y]){
                f[x][y]=f[y][x]=v;
                val[x][y]=val[y][x]=v;
            }
        }
        For(k,
 
1,n){
            For(i,1,k-2)
                For(j,i+1,k-1)
                    ans=min(ans,f[i][j]+val[i][k]+val[k][j]);
            For(i,1,n)
                For(j,1,n)
                    f[i][j]=min(f[i][j],f[i][k]+f[k][j]);
        }
        if(ans!=inf) o(ans),p('\n');
        else puts("It's impossible.");
    }
    return 0;
}