题意:求凸包的周长
#include
#include
#include
#include
using namespace std;
const double eps = 1e-8;
const double PI = acos(-1.0);
int sgn(double x) {
if(fabs(x) < eps)return 0;
if(x < 0)return -1;
else return 1;
}
struct Point {
double x,y;
Point() {}
Point(double _x,double _y) {
x = _x;
y = _y;
}
Point operator -(const Point &b)const {
return Point(x - b.x,y - b.y);
}
//叉积
double operator ^(const Point &b)const {
return x*b.y - y*b.x;
}
//点积
double operator *(const Point &b)const {
return x*b.x + y*b.y;
}
//绕原点旋转角度B(弧度值),后x,y的变化
void transXY(double B) {
double tx = x,ty = y;
x = tx*cos(B) - ty*sin(B);
y = tx*sin(B) + ty*cos(B);
}
};
double dist(Point a,Point b) {
return sqrt((a-b)*(a-b));
}
const int MAXN = 1010;
Point list[MAXN];
int Stack[MAXN],top;
//相对于list[0]的极角排序
bool _cmp(Point p1,Point p2) {
double tmp = (p1-list[0])^(p2-list[0]);
if(sgn(tmp) > 0)return true;
else if(sgn(tmp) == 0 && sgn(dist(p1,list[0]) - dist(p2,list[0])) <= 0)
return true;
else return false;
}
void Graham(int n) {
Point p0;
int k = 0;
p0 = list[0];
//找最下边的一个点
for(int i = 1; i < n; i++) {
if( (p0.y > list[i].y) || (p0.y == list[i].y && p0.x > list[i].x) ) {
p0 = list[i];
k = i;
}
}
swap(list[k],list[0]);
sort(list+1,list+n,_cmp);
if(n == 1) {
top = 1;
Stack[0] = 0;
return;
}
if(n == 2) {
top = 2;
Stack[0] = 0;
Stack[1] = 1;
return ;
}
Stack[0] = 0;
Stack[1] = 1;
top = 2;
for(int i = 2; i < n; i++) {
while(top > 1 &&
sgn((list[Stack[top-1]]-list[Stack[top-2]])^(list[i]-list[Stack[top-2]])) <=
0)
top--;
Stack[top++] = i;
}
}
int main(){
int n;
while(~scanf("%d",&n)&&n)
{
for(int i=0;ix),&((list+i)->y));
Graham(n);
double ans=0;
for(int i=1;i2) ans+=dist(list[Stack[0]],list[Stack[top-1]]);
printf("%.2fn",ans);
}
return 0;
}
未经允许不得转载!凸包 hdu1392