kruskal

#include <cstdio>
#include <iostream>
#include <algorithm>
#define inf 2000000000
using namespace std;
const int M=200004;
const int N=5005;
int n,m,tot;
struct NODE{
   
	int x,y,dis;
	bool operator < (const NODE &a){
   
		return this->dis < a.dis;
	}
}bian[M];
int fa[N];
inline int read(){
   
    int x=0,f=1;
    char ch=getchar();
    while(ch<'0'||ch>'9'){
   if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){
   x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
int find(int x){
   
	if(fa[x]==x) return fa[x];
	return find(fa[x]);
}
inline void kruskal(){
   
	tot=0;
	int ans=0;
	for(int i=1;i<=m;i++){
   
		if(fa[find(bian[i].x)]!=fa[find(bian[i].y)]){
   
			fa[find(bian[i].x)]=fa[find(bian[i].y)];
			tot++;
			ans=ans+bian[i].dis;
		}
		if(tot==n-1){
   
			printf("%d",ans);
			break;
		}
	}
	return ;
}
int main(){
   
	n=read();m=read();
	for(int i=1;i<=n;i++) fa[i]=i; 
    for(int i=1;i<=m;i++){
   
        int x,y,z;
        x=read();y=read();z=read();
        bian[i].x=x;bian[i].y=y;bian[i].dis=z;
    }
    sort(bian+1,bian+m+1);
    kruskal();
	return 0;
}

prim

#include <cstdio>
#include <iostream>
#include <algorithm>
#define inf 2000000000
using namespace std;
const int M=200004;
const int N=5005;
int n,m,tot;
bool vis[N];
int dis[N];
struct NODE{
   
    int to,nex,v;
}bian[M*2];
int head[M*2];
inline int read(){
   
    int x=0,f=1;
    char ch=getchar();
    while(ch<'0'||ch>'9'){
   if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){
   x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
inline void add(int x,int y,int z){
   
    bian[++tot].nex=head[x];
    bian[tot].to=y;
    bian[tot].v=z;
    head[x]=tot;
    return;
}
inline void prim(){
       
    int cnt=0,now=1;
    int minn=inf;
    int k,ans=0;
    for(int i=1;i<=n;i++) dis[i]=inf;
    dis[1]=0; vis[1]=1;
    for(int i=head[1];i;i=bian[i].nex){
   
    	dis[bian[i].to]=min(dis[bian[i].to],bian[i].v);
	}
    while(cnt<n-1){
   
        minn=inf;
        vis[now]=1;
        for(int i=1;i<=n;i++){
   
        	if(!vis[i]&&minn>dis[i]){
   
        		now=i;
        		minn=dis[i];
			}
		}
		ans=ans+minn;
          for(int i=head[now];i;i=bian[i].nex){
   
              if(!vis[bian[i].to]){
   
                    int lgr=bian[i].to;
                    if(bian[i].v<dis[lgr]){
   
                    	dis[lgr]=bian[i].v;
                    }
              }
          }
          cnt++;
    }
    printf("%d",ans); 
}
int main(){
   
    n=read();m=read();
    for(int i=1;i<=m;i++){
   
        int x,y,z;
        x=read();y=read();z=read();
        add(x,y,z);
        add(y,x,z);
    }
    prim();
    return 0;
}