Intersection(计算几何)
Intersection
Time Limit: 4000/4000 MS (Java/Others) Memory Limit: 512000/512000 K (Java/Others)
Total Submission(s): 3018 Accepted Submission(s): 1135
Problem Description
Matt is a big fan of logo design. Recently he falls in love with logo made up by rings. The following figures are some famous examples you may know.
A ring is a 2-D figure bounded by two circles sharing the common center. The radius for these circles are denoted by r and R (r < R). For more details, refer to the gray part in the illustration below.
Matt just designed a new logo consisting of two rings with the same size in the 2-D plane. For his interests, Matt would like to know the area of the intersection of these two rings.
Input
The first line contains only one integer T (T ≤ 105), which indicates the number of test cases. For each test case, the first line contains two integers r, R (0 ≤ r < R ≤ 10).
Each of the following two lines contains two integers xi, yi (0 ≤ xi, yi ≤ 20) indicating the coordinates of the center of each ring.
Output
For each test case, output a single line “Case #x: y”, where x is the case number (starting from 1) and y is the area of intersection rounded to 6 decimal places.
Sample Input
Sample Output
Source
2014ACM/ICPC亚洲区北京站-重现赛(感谢北师和上交)
//题意:问两个同样大的圆环相交的面积是多大
画图后,可以发现,用容斥定理很简单,area = 两个大圆的相交面积 - 2 * 大圆和小圆相交面积 + 两个小圆相交面积
求面积要用余弦定理,然后就简单了
#include <iostream>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <algorithm>
#include <map>
#include <stack>
#include <queue>
#include <set>
#include <vector>
using namespace std;
#define LL long long
#define PI acos(-1.0)
#define lowbit(x) (x&(-x))
#define INF 0x7f7f7f7f // 21 E
#define MEM 0x7f // memset 都变为 INF
#define MOD 4999 // 模
#define eps 1e-9 // 精度
#define MX 1000005 // 数据范围 int read() { //输入外挂
int res = , flag = ;
char ch;
if((ch = getchar()) == '-') flag = ;
else if(ch >= '' && ch <= '') res = ch - '';
while((ch = getchar()) >= '' && ch <= '') res = res * + (ch - '');
return flag ? -res : res;
}
// code... ... double area(double x1,double y1,double r1,double x2,double y2,double r2)
{
double d=(x1-x2)*(x1-x2)+(y1-y2)*(y1-y2);
if(d>=(r1+r2)*(r1+r2)) return ;
if(d<=(r1-r2)*(r1-r2)) return r1<r2 ? PI*r1*r1 : PI*r2*r2;
d=sqrt(d);
double a1=acos((r1*r1+d*d-r2*r2)/(2.0*r1*d));
double a2=acos((r2*r2+d*d-r1*r1)/(2.0*r2*d));
double s1=a1*r1*r1; //扇形s1
double s2=a2*r2*r2;
double sinx = sqrt(-cos(a1)*cos(a1));
double t = sinx * d * r1; //三角形
return s1+s2-t;
} int main()
{
int T;
cin>>T;
for (int cnt=;cnt<=T;cnt++)
{
double x1,y1,x2,y2,r1,r2;
scanf("%lf%lf",&r1,&r2);
scanf("%lf%lf",&x1,&y1);
scanf("%lf%lf",&x2,&y2);
double ans = area(x1,y1,r2,x2,y2,r2);
ans -= *area(x1,y1,r1,x2,y2,r2);
ans += area(x1,y1,r1,x2,y2,r1);
printf("Case #%d: %.6f\n",cnt,ans);
}
}
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