luogu P1111 修复公路 最小生成树prim

//稠密图
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int N = 100010, M = 200010, INF = 0x3f3f3f3f;
int n, m;
int p[N];
struct Edge {
    int a, b, w;
    bool operator< (const Edge &W)const {
        return w < W.w;
    }
} edges[M];
int find(int x) {
    if (p[x] != x) p[x] = find(p[x]);
    return p[x];
}
int kruskal() {
    sort(edges, edges + m);//每条边从小到大排序 ，找权重最小的边
    for (int i = 1; i <= n; i ++ ) p[i] = i;    // 初始化并查集
    int res = 0, cnt = 0;
    for (int i = 0; i < m; i ++ ) {
        int a = edges[i].a, b = edges[i].b, w = edges[i].w;
        a = find(a), b = find(b);
        if (a != b) {//如果不连通
            p[a] = b;
            res =max(w,res);
            cnt ++ ;
        }
    }
    if (cnt < n - 1) return -1;//说明不连通
    return res;
}
int main() {
    scanf("%d%d", &n, &m);
    for (int i = 0; i < m; i ++ ) {
        int a, b, w;
        scanf("%d%d%d", &a, &b, &w);
        edges[i] = {a, b, w};
    }
    int t = kruskal();
	cout<<t<<endl;
    return 0;
}