(+ Disjoint-set intersection circle)

Topic links: https://codeforces.com/gym/101915/problem/J

Ideas: all intersecting circles with disjoint-set maintenance seen as a whole, and then enumerate each of the left and right boundaries overall judgment can not cover the entire road at the same time.

AC Code:

 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 }