C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define N 100010
#define M 200010
struct Edge {
    int from, to;
    int weight;
} edges[M];
int n, m, father[N];

void init() {
    scanf("%d%d", &n, &m);
    for (int i = 0; i < m; ++i) {
        scanf("%d%d%d", &edges[i].from, &edges[i].to, &edges[i].weight);
    }
    for (int i = 1; i <= n; ++i) {
        father[i] = i;
    }
}

int findFather(int x) {
    if (father[x] != x) {
        father[x] = findFather(father[x]);
    }
    return father[x];
}

int cmpEdge(const void *lhs, const void *rhs) {
    struct Edge *pL = (struct Edge*) lhs, *pR = (struct Edge*) rhs;
    if (pL->weight > pR->weight) {
        return 1;
    } else if (pL->weight < pR->weight) {
        return -1;
    }
    return 0;
}

int Kruskal() {
    int ans = 0, cnt = 0;
    qsort(edges, m, sizeof(struct Edge), cmpEdge);

    for (int i = 0; i < m; ++i) {
        int u = edges[i].from, v = edges[i].to, w = edges[i].weight;
        int uFather = findFather(u), vFather = findFather(v);
        if (uFather == vFather) {
            continue;
        }
        father[uFather] = vFather;
        ans += w;
        ++cnt;
        if (cnt == n-1) {
            break;
        }
    }

    return cnt == n-1 ? ans : -1;
}

int main() {
    init();
    int res = Kruskal();
    if (res == -1) {
        puts("impossible");
    } else {
        printf("%d\n", res);
    }

    return 0;
}

C++

#include <iostream>
#include <queue>
#include <vector>
using namespace std;

const int N = 100010;
struct Edge {
    int from_, to_;
    int weight_;
    Edge(int from, int to, int weight) : from_(from), to_(to), weight_(weight) {}
    bool operator>(const Edge& rhs) const {
        return weight_ > rhs.weight_;
    }
};
int n, m;
vector<int> father(N);
priority_queue<Edge, vector<Edge>, greater<Edge> > pq;

void init() {
    cin >> n >> m;
    int u, v, w;
    while (m--) {
        cin >> u >> v >> w;
        pq.emplace(u, v, w);
    }

    for (int i = 1; i <= n; ++i) {
        father[i] = i;
    }
}

int findFather(int x) {
    if (father[x] != x) {
        father[x] = findFather(father[x]);
    }
    return father[x];
}

int Kruskal() {
    int ans = 0, cnt = 0;
    while (!pq.empty()) {
        auto [u, v, w] = pq.top();
        pq.pop();

        int uFather = findFather(u), vFather = findFather(v);
        if (uFather == vFather) {
            continue;
        }
        father[uFather] = vFather;
        ans += w;
        ++cnt;
        if (cnt == n-1) {
            break;
        }
    }

    return cnt == n-1 ? ans : -1;
}

int main() {
    init();
    if (int res = Kruskal(); res == -1) {
        cout << "impossible" << endl;
    } else {
        cout << res << endl;
    }

    return 0;
}