题意：https://codeforces.com/problemset/problem/281/C
就存个模板
1 #define IOS ios_base::sync_with_stdio(0); cin.tie(0);
2 #include <cstdio>//sprintf islower isupper
3 #include <cstdlib>//malloc exit strcat itoa system("cls")
4 #include <iostream>//pair
5 #include <fstream>//freopen("C:\\Users\\13606\\Desktop\\Input.txt","r",stdin);
6 #include <bitset>
7 //#include <map>
8 //#include<unordered_map>
9 #include <vector>
10 #include <stack>
11 #include <set>
12 #include <string.h>//strstr substr strcat
13 #include <string>
14 #include <time.h>// srand(((unsigned)time(NULL))); Seed n=rand()%10 - 0~9;
15 #include <cmath>
16 #include <deque>
17 #include <queue>//priority_queue<int, vector<int>, greater<int> > q;//less
18 #include <vector>//emplace_back
19 //#include <math.h>
20 #include <cassert>
21 #include <iomanip>
22 //#include <windows.h>//reverse(a,a+len);// ~ ! ~ ! floor
23 #include <algorithm>//sort + unique : sz=unique(b+1,b+n+1)-(b+1);+nth_element(first, nth, last, compare)
24 using namespace std;//next_permutation(a+1,a+1+n);//prev_permutation
25 //******************
26 clock_t __START,__END;
27 double __TOTALTIME;
28 void _MS(){__START=clock();}
29 void _ME(){__END=clock();__TOTALTIME=(double)(__END-__START)/CLOCKS_PER_SEC;cout<<"Time: "<<__TOTALTIME<<" s"<<endl;}
30 //***********************
31 #define rint register int
32 #define fo(a,b,c) for(rint a=b;a<=c;++a)
33 #define fr(a,b,c) for(rint a=b;a>=c;--a)
34 #define mem(a,b) memset(a,b,sizeof(a))
35 #define pr printf
36 #define sc scanf
37 #define ls rt<<1
38 #define rs rt<<1|1
39 typedef pair<int,int> PII;
40 typedef vector<int> VI;
41 typedef unsigned long long ull;
42 typedef long long ll;
43 typedef double db;
44 const db E=2.718281828;
45 const db PI=acos(-1.0);
46 const ll INF=(1LL<<60);
47 const int inf=(1<<30);
48 const db ESP=1e-9;
49 const int mod=(int)1e9+7;
50 const int N=(int)1e6+10;
51
52 bool zero(double x){
53 return (x>0?x:-x)<ESP;
54 }
55 struct point
56 {
57 double x,y;
58 };
59 struct line
60 {
61 point a,b;
62 };
63 //计算 cross product (P1-P0)x(P2-P0)
64 double xmult(point p1,point p2,point p0){
65 return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);
66 }
67 //计算 dot product (P1-P0).(P2-P0)
68 double dmult(point p1,point p2,point p0){
69 return (p1.x-p0.x)*(p2.x-p0.x)+(p1.y-p0.y)*(p2.y-p0.y);
70 }
71 //两点距离
72 double distance(point p1,point p2){
73 return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
74 }
75 bool isIntersected(point s1,point e1, point s2,point e2){
76 return (max(s1.x,e1.x) >= min(s2.x,e2.x))&&
77 (max(s2.x,e2.x) >= min(s1.x,e1.x))&&
78 (max(s1.y,e1.y) >= min(s2.y,e2.y))&&
79 (max(s2.y,e2.y) >= min(s1.y,e1.y))&&
80 (xmult(s1,s2,e1)*xmult(s1,e1,e2)>0)&&
81 (xmult(s2,s1,e2)*xmult(s2,e2,e1)>0);
82 }
83 point intersection(point u1,point u2,point v1,point v2){
84 point ret=u1;
85 double t=((u1.x-v1.x)*(v1.y-v2.y)-(u1.y-v1.y)*(v1.x-v2.x))
86 /((u1.x-u2.x)*(v1.y-v2.y)-(u1.y-u2.y)*(v1.x-v2.x));
87 ret.x+=(u2.x-u1.x)*t;
88 ret.y+=(u2.y-u1.y)*t;
89 return ret;
90 }
91
92
93 //点以原点逆时针旋转α度
94 point rotate(point p0,double alpha){
95 alpha=alpha/180*PI;
96 return {p0.x*cos(alpha)-p0.y*sin(alpha),p0.y*cos(alpha)+p0.x*sin(alpha)};
97 }
98
99 point Pin[20];
100 int cmp(point a,point b) ///设<p1,p2,...pm>为对其余点按以p0为中心的极角逆时针排序所得的点集（如果有多个点有相同的极角，除了距p0最远的点外全部移除)
101 {
102 if(xmult(a,b,Pin[1])>ESP)
103 return 1;
104 if(fabs(xmult(a,b,Pin[1]))<ESP&&distance(b,Pin[1])-distance(a,Pin[1])>ESP)
105 return 1;
106 return 0;
107 }
108
109 point Stack[N];
110 int top;
111 void Graham(int n,point p[])
112 {
113 top=3;///栈顶在2，因为凸包的前两个点是不会变了
114 sort(p+2,p+1+n,cmp);
115 Stack[1]=p[1];///压p0p1p2进栈S
116 Stack[2]=p[2];
117 Stack[3]=p[3];
118 for(int i=4;i<=n;i++){
119 while(top>=1&&xmult(p[i],Stack[top],Stack[top-1])>ESP){///有了更好的选择
120 top--;
121 }
122 Stack[++top]=p[i];
123 }
124 }
125 double getArea()
126 {
127 double sum=fabs(xmult(Stack[2],Stack[3],Stack[1]));
128 for(int i=3;i<top;i++)
129 sum+=fabs(xmult(Stack[i],Stack[i+1],Stack[1]));
130 return sum/2.0;
131 }
132
133 int main()
134 {
135 double w,h,alpha;
136 sc("%lf%lf%lf",&w,&h,&alpha);
137 if(alpha==0||alpha==180)
138 {
139 pr("%.10lf\n",w*h);
140 return 0;
141 }
142 if(alpha==90&&w==h)
143 {
144 pr("%.10lf\n",w*h);
145 return 0;
146 }
147 line line1[10];
148 point p1={-w/2,h/2};
149 point p2={w/2,h/2};
150 point p3={w/2,-h/2};
151 point p4={-w/2,-h/2};
152 line1[1]={p1,p2};
153 line1[2]={p2,p3};
154 line1[3]={p3,p4};
155 line1[4]={p4,p1};
156
157 line line2[10];
158 p1=rotate(p1,alpha);
159 p2=rotate(p2,alpha);
160 p3=rotate(p3,alpha);
161 p4=rotate(p4,alpha);
162 line2[1]={p1,p2};
163 line2[2]={p2,p3};
164 line2[3]={p3,p4};
165 line2[4]={p4,p1};
166
167 int cp=0;
168 for(int i=1;i<=4;++i)
169 {
170 for(int j=1;j<=4;++j)
171 {
172 if(isIntersected(line1[i].a,line1[i].b,line2[j].a,line2[j].b))
173 Pin[++cp]=intersection(line1[i].a,line1[i].b,line2[j].a,line2[j].b);
174 }
175 }
176 // for(int i=1;i<=cp;++i)pr("%lf\t%lf\n",Pin[i].x,Pin[i].y);
177 Graham(cp,Pin);
178 pr("%.10lf\n",getArea());
179 return 0;
180 }
181
182 /**************************************************************************************/
原文地址：https://www.cnblogs.com/--HPY-7m/p/12687822.html
时间： 2024-10-16 22:37:40