AC程式碼：

#include <bits/stdc++.h>

using namespace std;

const int maxn = 1e5 + 5;
const int Mod = 1e9 + 7;
const int INF = 0x3f3f3f3f;
#define LL long long

struct Edge{
    int v, w, nxt;
}edge[maxn * 20], Heap[maxn * 20];

int tot, head[maxn << 1];
int hlength, n, m;

void init(){
    hlength =
 
 tot = 0;
    memset(head, -1, sizeof(head));
}

void addEdge(int u, int v, int w) {
    edge[tot].v = v;
    edge[tot].w = w;
    edge[tot].nxt = head[u];
    head[u] = tot ++;

    edge[tot].v = u;
    edge[tot].w = w;
    edge[tot].nxt = head[v];
    head[v] = tot ++;
}

void down(int p) {
    int
 
 q = p * 2;
    Edge a = Heap[p];
    while(q <= hlength) {
        if(q < hlength && Heap[q].w > Heap[q + 1].w) q ++;
        if(Heap[q].w >= a.w) break;
        else {
            Heap[p] = Heap[q];
            p = q;
            q = p * 2;
        }
    }
    Heap[p] = a;
}

void
 
 up(int p) {
    int q = p/2;
    Edge a = Heap[p];
    while(q >= 1 && a.w < Heap[q].w) {
        Heap[p] = Heap[q];
        p = q;
        q = p/2;
    }
    Heap[p] = a;
}

void insert(Edge a) {
    Heap[++ hlength] = a;
    up(hlength);
}

Edge getMin() {
    Edge r = Heap[1];
    Heap[1] = Heap[hlength --];
    down(1);
    return r;
}

int ans = 0;
int dis[maxn], vis[maxn];
void Prim() {
     memset(dis, INF, sizeof(dis));
     memset(vis, 0, sizeof(vis));
     dis[1] = 0;
     insert({1, 0, -1});
     while(hlength) {
        Edge t = getMin();
        if(vis[t.v]) continue;
        ans += t.w;
        vis[t.v] = 1;
        for (int i = head[t.v]; i + 1; i = edge[i].nxt) {
            if(!vis[edge[i].v] && dis[edge[i].v] > edge[i].w) {
                dis[edge[i].v] = edge[i].w;
                insert({edge[i].v, edge[i].w, -1});
            }
        }
     }
}

int main()
{
    init();
    scanf("%d %d", &n, &m);
    for (int i = 0; i < m; i ++) {
        int u, v, w;
        scanf("%d %d %d", &u, &v, &w);
        addEdge(u, v, w);
    }
    Prim();
    cout << ans << endl;
    return 0;
}