最小生成树 - 克鲁斯卡尔 - 并查集 - 边稀疏 - O(E * logE)

 

#define _CRT_SECURE_NO_WARNINGS
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
#define N 100005
int p[N];

struct Edge
{
    int s, e;
    int cost;
}edge[N];

bool cmp(struct Edge a, struct Edge b)
{
    return a.cost < b.cost;
}

int getPar(int k)
{
    if (p[k] == k)
        return k;
    return p[k] = getPar(p[k]);
}

int main()
{
    int n, m, ans, i, k;
    scanf("%d%d", &n, &m);
    for (i = 0; i < m; i++)
        scanf("%d%d%d", &edge[i].s, &edge[i].e, &edge[i].cost);
    sort(edge, edge + m, cmp);
    for (i = 1; i <= n; i++)
        p[i] = i;
    for (ans = 0, k = 0, i = 0; i < m && k < n-1; i++)
    {
        int ps = getPar(edge[i].s), pe = getPar(edge[i].e);
        if (ps == pe)
            continue;
        p[ps] = pe;
        ans += edge[i].cost;
        k++;
    }
    printf("%d\n", ans);
    return 0;
}