蒟蒻最小生成树prim 42pts，求dalao解答

#include <iostream>
#include <cstring>
#include <queue>
#include <cmath>

using namespace std;

const int N = 1e3 + 10;

struct node {
	double x, y;
};

int n;
node a[N];
bool vis[N];
double dis[N];
double ans; 

void prim() {
	for (int i = 1; i <= n; i++) dis[i] = 1e9;
	priority_queue<pair<double, int>, vector<pair<double, int> >, greater<pair<double, int> > > pq;
	pq.push({0, 1});
	dis[1] = 0;
	int cnt = 0;
	while (!pq.empty()) {
		if (cnt >= n) return;
		int x = pq.top().second;
		pq.pop();
		if (vis[x]) continue;
		vis[x] = true;
		cnt++;
		for (int y = 1; y <= n; y++) {
			if (y == x) continue;
			double d = sqrt((a[y].x - a[x].x) * (a[y].x - a[x].x) + (a[y].y - a[x].y) * (a[y].y - a[x].y));
			if (d < dis[y]) {
				dis[y] = d;
				pq.push({d, y});
			}
		}
	}
} 
int main() {
	cin >> n;
	for (int i = 1; i <= n; i++)
		cin >> a[i].x >> a[i].y;
	prim();
	for (int i = 1; i <= n; i++)
		ans = max(ans, dis[i]);
	printf("%.7f\n", ans / 2);
	return 0;
}