prim
朴素prim
#include<bits/stdc++.h>
using namespace std;
const int N = 550, INF = 0x3f3f3f3f;
int n, m, dis[N], g[N][N];
bool vis[N];
int prim()
{
memset(dis, 0x3f, sizeof dis);
int res = 0;
for(int i = 0; i < n; i ++ )
{
int t = -1;
for(int j = 1; j <= n; j ++ )
if(!vis[j] && (t == -1 || dis[j] < dis[t])) t = j;
if(i && dis[t] == INF) return INF;
if(i) res += dis[t];
vis[t] = true;
for(int j = 1; j <= n; j ++ )
dis[j] = min(dis[j], g[j][t]);
}
return res;
}
int main()
{
cin >> n >> m;
memset(g, 0x3f, sizeof g);
while(m -- )
{
int f, t, l;
cin >> f >> t >> l;
g[f][t] = g[t][f] = min(g[t][f], l);
}
int t = prim();
if(t == INF) puts("impossible");
else cout << t << endl;
return 0;
}