计算出圆心到原点的距离以后 加减 圆的半径，跟圆环的内外半径比较就好了
#include <iostream> #include <cstdio> #include <cstdlib> #include <cstring> #include <string> #include <cmath> #include <set> #include <map> #include <stack> #include <queue> #include <ctype.h> #include <vector> #include <algorithm> #include <sstream> #define PI acos(-1.0) #define in freopen("in.txt", "r", stdin) #define out freopen("out.txt", "w", stdout) using namespace std; typedef long long ll; const int maxn = 500 + 7, INF = 0x3f3f3f3f, mod = 1e9 + 7; int r1, d, r2, n; double dd(int x, int y) { return sqrt(x*x + y*y); } int main() { scanf("%d %d%d", &r1, &d, &n); r2 = r1 - d; int ans = 0, x, y; double rr; for(int i = 0; i < n; ++i) { scanf("%d%d%lf", &x, &y, &rr); double t = dd(x, y); if(t-rr >= r2 && t+rr <= r1) ans++; } cout << ans << endl; return 0; }
