最小生成树kruskal

AcWing 859. Kruskal算法求最小生成树

#include <iostream>
#include <algorithm>

using namespace std;

const int N = 1e5 + 10, M = N * 2;
int n, m;
int f[N];

struct node
{
    int x, y, w;
}a[M];

int cmp(node x, node y)
{
    return x.w < y.w;    
}

int root(int x)
{
    if (x != f[x]) f[x] = root(f[x]);
    return f[x];
}


int main()
{
    cin >> n >> m;

    for (int i = 0; i < m; i ++ ) cin >> a[i].x >> a[i].y >> a[i].w;

    sort(a, a + m, cmp);

    int cnt = 0, sum = 0;
    for (int i = 1; i <= n; i ++ ) f[i] = i;

    for (int i = 0; i < m; i ++ )
    {
        int fx = root(a[i].x), fy = root(a[i].y);

        if (fx != fy)
        {
            cnt ++ ;
            sum += a[i].w;
            f[fx] = fy;
        }
    }

    if (cnt != n - 1) cout << "impossible";
    else cout << sum;

    return 0;
}