672
POJ 3348 求凸包麵積
題意給出n個點求凸包，然後求出凸包麵積就可以。
模板題求出凸包後用叉積求出麵積就可以了。
#include <iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
typedef int PointType;
struct point
{
PointType x,y;
int num;
};
point data[10005],stack[10005],MinA;
int top;
PointType Direction(point pi,point pj,point pk) //判斷向量PiPj在向量PiPk的順逆時針方向 +順-逆0共線
{
return (pj.x-pi.x)*(pk.y-pi.y)-(pk.x-pi.x)*(pj.y-pi.y);
}
PointType Dis(point a,point b)
{
return (a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y);
}
bool cmp(point a,point b)
{
PointType k=Direction(MinA,a,b);
if(k>0) return 1;
if(k<0) return 0;
return Dis(MinA,a)>Dis(MinA,b);
}
int ab(int a)
{
return a>=0?a:-a;
}
void Graham_Scan(point *a,int numa)
{
for(int i=0; i<numa; i++)
if(a[i].y<a[0].y||(a[i].y==a[0].y&&a[i].x<a[0].x))
swap(a[i],a[0]);
MinA=a[0],top=0;
sort(a+1,a+numa,cmp);
stack[top++]=a[0],stack[top++]=a[1],stack[top++]=a[2];
for(int i=3; i<numa; i++)
{
while(Direction(stack[top-2],stack[top-1],a[i])<0)
top--;
stack[top++]=a[i];
}
}
int main()
{
int n;
while(~scanf("%d",&n))
{
for(int i=0; i<n; i++)
scanf("%d%d",&data[i].x,&data[i].y);
if(n<3)
{
puts("0");
continue;
}
Graham_Scan(data,n);
int sum=0;
for(int i=1; i<top-1; i++)
sum+=ab(Direction(stack[0],stack[i],stack[i+1]));
printf("%d\n",sum/100);
}
return 0;
}
最後更新：2017-04-03 22:15:30