2429: [HAOI2006]聪明的猴子 (生成树)

#include<algorithm>
#include<iostream>
#include<cstdio>
using namespace std;

inline int read() {
int x = 0, f = 1;
char ch = getchar();
while (ch < '0' || ch > '9') {
if (ch == '-')f = -1;
ch = getchar();
}
while (ch >= '0' && ch <= '9') {
x = x * 10 + ch - '0';
ch = getchar();
}
return x*f;
}

struct edge {
int x, y, v;
} e[500001];
int n, m, tot, cnt, mx, ans, fa[1001], a[501], x[1001], y[1001];

inline bool cmp(edge a, edge b) {
return a.v < b.v;
}

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

int main() {
m = read();
for (int i = 1; i <= m; i++)
a[i] = read();
n = read();
for (int i = 1; i <= n; i++) {
fa[i] = i;
x[i] = read();
y[i] = read();
}
for (int i = 1; i < n; i++)
for (int j = i + 1; j <= n; j++)
e[++cnt] = (edge){i, j, (x[i] - x[j])*(x[i] - x[j])+(y[i] - y[j])*(y[i] - y[j])};
sort(e + 1, e + cnt + 1, cmp);
for (int i = 1; i <= cnt; i++) {
int p = find(e[i].x), q = find(e[i].y);
if (p != q) {
fa[p] = q;
tot++;
if (tot == n - 1) {
mx = e[i].v;
break;
}
}
}
for (int i = 1; i <= m; i++)
if (a[i] * a[i] >= mx)
ans++;
printf("%d", ans);
return 0;
}