记录下生成树的每条边，

然后从每个边开始找次小边，

再求出严格最小值

#include<algorithm>
#include<cstring>
#include<cstdio>
using namespace std;
#define re register
#define M 5005
#define N 200005
#define il inline
#define edge a
il int read(){re int x=0,f=1;char c=getchar();while(c<'0'||c>'9'){if(c=='-') f=-1;c=getchar();}while(c>='0'&&c<='9') x=(x<<3)+(x<<1)+(c^48),c=getchar();return x*f;}
struct Edge{
	int u,v,w;
}edge[N];
int fa[M],tot,mark[N],val[N],vall=0x7fffff,sb=0x7fffff,n,m,ans,eu,ev,cnt,cans=0x7fffffff,head[N],to[N],nxt[N];
il void add(int u,int v,int w){
	to[++tot]=v;
	nxt[tot]=head[u];
	head[u]=tot;
	val[tot]=w;
} 
il bool cmp(Edge a,Edge b){
    return a.w<b.w;
}
il int find(int x){
    while(x!=fa[x]) x=fa[x]=fa[fa[x]];
    return x;
}
il void kruskal(){
    sort(edge,edge+m,cmp);
    for(re int i=0;i<m;i++){
        eu=find(edge[i].u), ev=find(edge[i].v);
        if(eu==ev)continue;
        ans+=edge[i].w;
        fa[ev]=eu;
		  mark[++cnt]=i; 
        if(cnt==n-1){
            break;
        }
    }
}
int main(){
    n=read(),m=read();
    for(re int i=1;i<=n;i++)fa[i]=i;
    for(re int i=0;i<m;i++){
    	edge[i].u=read(),edge[i].v=read(),edge[i].w=read();
    	add(edge[i].u,edge[i].v,edge[i].w);
    	add(edge[i].v,edge[i].u,edge[i].w);
    }
    kruskal();
    bool flg=0;
    for(int i=1;i<=cnt;i++){
		sb=a[mark[i]].w,vall=0x7ffff;	
    	for(int j=head[a[mark[i]].u];j;j=nxt[j]){
    		int y=to[j];
    		if(y==a[mark[i]].v)continue;
    		vall=min(vall,val[j]);
    	}
    	if(sb==vall)continue;
    	flg=1;
    	cans=min(ans-sb+vall,cans);
    }
    if(flg==0)cans=ans;
    printf("%d",cans);
    return 0;
}