最后一个测试点错了，急84分！！！

#include<bits/stdc++.h>
using namespace std;
struct node {
    int x, y, c;
} a[500010];
int n, m, f[500010], ans, t;
int g(int x) {
    if (f[x] == x) return x;
    else {
        f[x] = g(f[x]);
        return f[x];
    }
}
bool cmp(node a, node b) {
    return a.c < b.c;
}
int main() {
    cin>>n>>m;
    for (int i = 1; i <= n; i++) f[i] = i;
    for (int i = 1; i <= m; i++){
        cin>>a[i].x>>a[i].y>>a[i].c;
    }
    sort(a + 1, a + m + 1, cmp);
    for (int i = 1; i <= m; i++) {
        int fx, fy;
        fx = g(a[i].x);
        fy = g(a[i].y);
        if (fx != fy) {
            ans += a[i].c;
            t++;
            f[fy] = fx;
            if (t == n - 1) break;
        }
    }
    cout<<ans;
    return 0;
}

测试点 ！！！！！！！！！！！！！！！！！！！