不正经题解|圆-切线

就是一道简单数学题，对各种情况进行分析即可，代码：

#include <iostream>
#include <cmath>
#include <algorithm>
using namespace std;
double Len(int x1,int y1,int x2,int y2) {
	return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}
int main() {
	int T;
	scanf("%d",&T);
	while (T--) {
		int x1,y1,r1,x2,y2,r2;
		scanf("%d %d %d%d %d %d",&x1,&y1,&r1,&x2,&y2,&r2);
		double k=Len(x1,y1,x2,y2);
		if (r1==r2) {
			if (k>r1+r2) {
				printf("4\n");
			}else if (k==r1+r2) {
				printf("3\n");
			}else if (k>0){
				printf("2\n");
			}else {
				printf("INF\n");
			}
		}else {
			if (k>r1+r2) {
				printf("4\n");
			}else if (k==r1+r2) {
				printf("3\n");
			}else if (k>abs(r1-r2)) {
				printf("2\n");
			}else if (k==abs(r1-r2)) {
				printf("1\n");
			}else {
				printf("0\n");
			}
		}
	}
	return 0;
}