CodeForces

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;}