Kruskal算法

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
#define N 510

int pre[N];

class edge{
public:
	int u, v, value;
};

bool cmp(const edge& a, const edge& b) {
	return a.value < b.value;
}

vector<edge> v;

int unionsearch(int x) {
	return pre[x] = pre[x] == x ? x : unionsearch(pre[x]);
}

bool join(int u, int v) {
	int root1 = unionsearch(u);
	int root2 = unionsearch(v);
	if (root1 == root2)
		return false;
	pre[root1] = root2;
	return true;
}

int main() {
	int i, num_vertex, num_edge, local_edge, ans;
	edge tmp;

	v.clear();
	cin >> num_vertex >> num_edge;

	for (i = 1; i <= num_vertex; i++)
		pre[i] = i;
	ans = local_edge = 0;
	for (i = 0; i < num_edge; i++) {
		cin >> tmp.u >> tmp.v >> tmp.value;
		v.push_back(tmp);
	}
	sort(v.begin(), v.end(), cmp);
	for (i = 0; i < num_edge && local_edge < num_vertex - 1; i++) 
		if (join(v[i].u, v[i].v)) {
			local_edge++;
			ans += v[i].value;
		}

	cout << ans << endl;
	return 0;
}