【BZOJ3479】[Usaco2014 Mar]Watering the Fields【最小生成树】

【题目链接】

/* Pigonometry */
#include 
#include 
#include 

using namespace std;

const int maxn = 2005, maxm = 2000005;

int n, c, fa[maxn];

struct _point {
	int x, y;
} p[maxn];

struct _edge {
	int u, v, w;

	bool operator < (const _edge &x) const {
		return w < x.w;
	}
} g[maxm];

inline int iread() {
	int f = 1, x = 0; char ch = getchar();
	for(; ch < '0' || ch > '9'; ch = getchar()) f = ch == '-' ? -1 : 1;
	for(; ch >= '0' && ch <= '9'; ch = getchar()) x = x * 10 + ch - '0';
	return f * x;
}

inline int dis(_point a, _point b) {
	return (a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y);
}

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

int main() {
	n = iread(); c = iread();
	for(int i = 1; i <= n; i++) fa[i] = i, p[i] = (_point){iread(), iread()};

	int tot = 0;
	for(int i = 1; i <= n; i++) for(int j = i + 1; j <= n; j++) {
		int d = dis(p[i], p[j]);
		if(d >= c) g[++tot] = (_edge){i, j, d};
	}
	sort(g + 1, g + 1 + tot);

	int cnt = 0, ans = 0;
	for(int i = 1; i <= tot && cnt != n - 1; i++) {
		int u = find(g[i].u), v = find(g[i].v);
		if(u ^ v) {
			cnt++;
			ans += g[i].w;
			fa[u] = v;
		}
	}

	if(cnt != n - 1) printf("-1\n");
	else printf("%d\n", ans);

	return 0;
}