第一次写凸包的代码,虽然过了,但是这个原理emmmm...
用的Graham和Andrew算法,记录下来方便以后看吧。。
1.POJ1113 Wall 凸包
就是用的kuangbin的模板,附AC代码:
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<iostream>
#include<algorithm>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<queue>
#include<string>
#include<sstream>
#include<fstream>
#include<utility>
using namespace std;
#define ll long long
typedef pair<int,int>pp;
const double pi=acos(-1.0);
const double eps=1e-9;
const int INF=0x3f3f3f3f;
const ll MOD=1e9+7ll;
const int MAX=1005;
int n,l;
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);
}
double operator ^(const point &b)const //叉积
{
return x*b.y-y*b.x;
}
double operator *(const point &b)const //点积
{
return x*b.x+y*b.y;
}
void transXY(double B)
{
double tx=x,ty=y;
x=tx*cos(B)-ty*sin(B);
y=tx*sin(B)+ty*cos(B);
}
}p[MAX];
int s[MAX],top;
int sgn(double x)
{
if(fabs(x)<eps)
return 0;
else if(x<0)
return -1;
else
return 1;
}
double dist(struct point a,struct point b)
{
return sqrt((a-b)*(a-b));
}
bool cmp(struct point p1,struct point p2)
{
double tmp=(p1-p[0])^(p2-p[0]);
if(sgn(tmp)>0)
return true;
else if(sgn(tmp)==0&&sgn(dist(p1,p[0])-dist(p2,p[0]))<=0)
return true;
else
return false;
}
void Graham()
{
int k=0;
point p0=p[0];
for(int i=1;i<n;i++)
if((p0.y>p[i].y)||(p0.y==p[i].y&&p0.x>p[i].x))
{
p0=p[i];
k=i;
}
swap(p[k],p[0]);
sort(p+1,p+n,cmp);
if(n==1)
{
top=1;
s[0]=0;
return;
}
if(n==2)
{
top=2;
s[0]=0;s[1]=1;
return;
}
top=2;
s[0]=0;s[1]=1;
for(int i=2;i<n;i++)
{
while(top>1&&sgn((p[s[top-1]]-p[s[top-2]])^(p[i]-p[s[top-2]]))<=0)
top--;
s[top++]=i;
}
//top--;
}
int main()
{
while(~scanf("%d%d",&n,&l))
{
for(int i=0;i<n;i++)
scanf("%lf%lf",&p[i].x,&p[i].y);
sort(p,p+n,cmp);
Graham();
double ans=0;
ans+=2*pi*l;
for(int i=0;i<top-1;i++)
ans+=dist(p[s[i]],p[s[i+1]]);
ans+=dist(p[s[top-1]],p[s[0]]);
printf("%.0f\n",ans);
//printf("%d\n",int(res+0.5));
}
return 0;
}
2.CodeForces-166B Polygons 凸包+二分
这道题一开始想的是求凸包+判断点是否在凸包上,但是数据量太大了就不行。。
然后贴大佬博客Orz:https://blog.csdn.net/xuh723/article/details/22451957
记录下来这道题主要也是因为学到了一种快速二分查找的函数:lower_bound()
大佬用了Andrew算法,感觉都差不多吧,但是因为我没学过C++运算符重载,用上面的模板时总是出问题,lower_bound()也总是报错。后来发现两个函数cmp的方式和"<"号的定义方式不一样,因此出现了那么多问题...所以最后还是直接copy大佬的模板了_(:з」∠)_
附上最后AC的代码:
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<iostream>
#include<algorithm>
using namespace std;
#define ll long long
const double eps=1e-9;
const int INF=0x3f3f3f3f;
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);
}
bool operator <(const point &b) const
{
return x<b.x||x==b.x&&y<b.y;
}
};
int sgn(double x)
{
if(fabs(x)<eps)
return 0;
else if(x<0)
return -1;
else
return 1;
}
double cross(point a,point b)
{
return a.x*b.y-b.x*a.y;
}
const int MAX=2e5+5;
int n,m;
point p[MAX],pb[20005];
point s[MAX];
int top;
void andrew(int n)
{
sort(p,p+n);
top=0;
for(int i=0;i<n;i++)
{
while(top>1&&cross(s[top-1]-s[top-2],p[i]-s[top-2])<0)
top--;
s[top++]=p[i];
}
int k=top;
for (int i=n-2;i>=0;--i)
{
while(top>k&&cross(s[top-1]-s[top-2],p[i]-s[top-2])<0)
top--;
s[top++]=p[i];
}
if(top>1)
top--;
}
int main()
{
while(~scanf("%d",&n))
{
for(int i=0;i<n;i++)
scanf("%lf%lf",&p[i].x,&p[i].y);
scanf("%d",&m);
for(int i=n;i<n+m;i++)
{
scanf("%lf%lf",&p[i].x,&p[i].y);
pb[i-n]=p[i];
}
andrew(n+m);
sort(pb,pb+m);
int i;
for(i=0;i<top;i++)
{
int pos=lower_bound(pb,pb+m,s[i])-pb;//返回第一个大于等于s[i]的pb的下标
if((sgn(pb[pos].x-s[i].x)==0)&&(sgn(pb[pos].y-s[i].y)==0))
break;
}
if(i==top)
printf("YES\n");
else
printf("NO\n");
}
return 0;
}
同时也想说没好好学过C++真是难过啊QAQ...
那个运算符重载。。真是不懂啊555555...