【模板】Kruskal重构树

备注相关试题：1.货车运输

#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 2;
const int M = 1e6 + 2;
int n, m, wcnt;
int son[N << 1][2], fa[N << 1];
int val[N << 1];
struct Edge {
	int u, v, w;
} e[M];

int fifa(int x) {
	return (fa[x] == x) ? x : fa[x] = fifa(fa[x]);
}

void Build() {
	int sum = 0, wcnt = n;

	for (int i = 1; i <= m; i++) {
		
		int u = e[i].u, v = e[i].v, w = e[i].w;
		int fau = fifa(fa[u]);
		int fav = fifa(fa[v]);
		if (fau == fav) continue;
		
		fa[fau] = fa[fav] = ++wcnt;
		
		fa[wcnt] = wcnt;
		son[wcnt][0] = fau;
		son[wcnt][1] = fav;
		val[wcnt] = w;
		
		sum++;
		if (sum == n - 1) break;
	}
}

int main() {
	scanf("%d%d", &n, &m);

	for (int i = 1; i <= n; i++) fa[i] = i;

	int u, v, w;
	for (int i = 1; i <= m; i++) {
		scanf("%d%d%d", &u, &v, &w);
		e[i].u = u;
		e[i].v = v;
		e[i].w = w;
	}
	sort(e + 1, e + 1 + m, [](Edge x, Edge y) {
		return x.w > y.w;
	});
	Build();
	return 0;
}