prim

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<string>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<stack>
using namespace std;
const int inf=0xffffff;
const int MAXN=21;
int edges[MAXN][MAXN];
int lowcost[MAXN];
int nearvex[MAXN];
int n,m;
void prim(int u0)
{
    int i,j;
    int sum=0;
    for(i=1;i<=n;i++)
    {
        lowcost[i]=edges[u0][i];
        nearvex[i]=u0;
    }
    nearvex[u0]=-1;
    for(i=1;i<n;i++)            //找出n-1个顶点 
    {
        int min=inf;
        int v=-1;
        for(j=1;j<=n;j++)
        {
            if(nearvex[j]!=-1&&lowcost[j]<min)
            {
                v=j;
                min=lowcost[j];
            }
        }
        if(v!=-1)
        {
            printf("%d %d %d
",nearvex[v],v,lowcost[v]);
            nearvex[v]=-1;
            sum+=lowcost[v];
            for(j=1;j<=n;j++)
            {
                if(nearvex[j]!=-1&&edges[v][j]<lowcost[j])
                {
                    lowcost[j]=edges[v][j];
                    nearvex[j]=v;
                }
            }
        }
    }
}
int main()
{
    int i,j;
    int u,v,w;
    scanf("%d %d",&n,&m);
    memset(edges,0,sizeof(edges));
    for(i=1;i<=m;i++)
    {
        scanf("%d%d%d",&u,&v,&w);
        edges[u][v]=edges[v][u]=w;
    }
    for(i=1;i<=n;i++)
        for(j=1;j<=n;j++)
        {
            if(i==j)
                edges[i][j]=0;
            else if(edges[i][j]==0)
                edges[i][j]=inf;
        }
    prim(1);
    return 0;
}