题目链接：https://codeforces.com/gym/101915/problem/J
思路：将所有相交的圆用并查集维护看做一个整体，然后枚举每个整体的左边界和右边界，判断能不能同时覆盖整个路。
AC代码：
1 #include<bits/stdc++.h>
2 using namespace std;
3 typedef long long ll;
4 const int maxn = 1e5 + 5;
5 int n;
6 struct circle{
7 ll x, y, r;
8 };
9 circle c[maxn];
10 bool intercircle(circle a, circle b)
11 {
12 ll d = (a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y);
13 ll r = a.r + b.r;
14 if(d <= r * r) return true;
15 else return false;
16 }
17 int far[maxn], L[maxn], R[maxn];
18 int find(int x)
19 {
20 if(far[x] == x) return x;
21 else return far[x] = find(far[x]);
22 }
23 void unite(int x, int y)
24 {
25 x = find(x);
26 y = find(y);
27 if(x == y) return;
28 far[x] = y;
29 }
30 void init(int n)
31 {
32 for(int i = 0;i <= n;i++)
33 {
34 far[i] = i;
35 L[i] = R[i] = 0;
36 }
37 }
38 int main()
39 {
40 std::ios::sync_with_stdio(false);
41 int t;
42 cin >> t;
43 while(t--)
44 {
45 ll w, l;
46 cin >> n >> w >> l;
47 init(n);
48 for(int i = 0;i < n;i++) cin >> c[i].x >> c[i].y >> c[i].r;
49 for(int i = 0;i < n;i++)
50 {
51 for(int j = 0;j < i;j++)
52 {
53 if(intercircle(c[i],c[j])) unite(i, j);
54 }
55 }
56 for(int i = 0;i < n;i++)
57 {
58 if(c[i].x - c[i].r <= 0) L[find(i)] = 1;
59 if(c[i].x + c[i].r >= w) R[find(i)] = 1;
60 }
61 int ans = 0;
62 for(int i = 0;i < n;i++)
63 {
64 if(L[i] && R[i]) ans++;
65 }
66 cout << ans << endl;
67 }
68 return 0;
69 }