[Codeforces50C]Happy Farm 5 凸包

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大致題意：

　　平面上有n個整數點，問你最少經過多少步能夠將所有點嚴格包圍。

　　將點嚴格包圍要求你走的路徑完全包圍給出的點且不能有點在路徑上

　　你只能走整數點，且方向只有上下左右左上右下等8個方向，每次移動一格。

 

答案

　　先對點構造凸包，答案即為每條邊 max(abs(x1-x2),abs(y1-y2))的累加和+4；

　　

#include<cstdio>#include<iostream>#include<cstring>#include<algorithm>#include<queue>#include<set>#include<map>#include<stack>#include<time.h>#include<cstdlib>#include<cmath>#include<list>using namespace std;#define MAXN 100100#define eps 1e-9#define For(i,a,b) for(int i=a;i<=b;i++) #define Fore(i,a,b) for(int i=a;i>=b;i--) #define lson l,mid,rt<<1#define rson mid+1,r,rt<<1|1#define mkp make_pair#define pb push_back#define cr clear()#define sz size()#define met(a,b) memset(a,b,sizeof(a))#define iossy ios::sync_with_stdio(false)#define fre freopen#define pi acos(-1.0)#define inf 1e6+7#define Vector Pointconst int Mod=1e9+7;typedef unsigned long long ull;typedef long long ll;int dcmp(double x){    if(fabs(x)<=eps) return 0;    return x<0?-1:1;}struct Point{    double x,y;    Point(double x=0,double y=0):x(x),y(y) {}    bool operator < (const Point &a)const{        if(x==a.x) return y<a.y;        return x<a.x;    }    Point operator - (const Point &a)const{        return Point(x-a.x,y-a.y);    }    Point operator + (const Point &a)const{        return Point(x+a.x,y+a.y);    }    Point operator * (const double &a)const{        return Point(x*a,y*a);    }    Point operator / (const double &a)const{        return Point(x/a,y/a);    }    void read(){        scanf("%lf%lf",&x,&y);    }    void out(){        cout<<"debug: "<<x<<" "<<y<<endl;    }    bool operator == (const Point &a)const{        return dcmp(x-a.x)==0 && dcmp(y-a.y)==0;    }};double Dot(Vector a,Vector b) {    return a.x*b.x+a.y*b.y;}double dis(Vector a) {    return sqrt(Dot(a,a));}double Cross(Point a,Point b){    return a.x*b.y-a.y*b.x;}int ConvexHull(Point *p,int n,Point *ch){    int m=0;    For(i,0,n-1) {        while(m>1 && Cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0) m--;        ch[m++]=p[i];    }    int k=m;    Fore(i,n-2,0){        while(m>k && Cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0) m--;        ch[m++]=p[i];    }    if(n>1) m--;    return m;}bool cmp(Point a,Point b){    return a.y<b.y;}int n,m;Point p[100005];Point ch[100005];void solve(){    cin>>n;    int ans=0;    For(i,0,n-1) p[i].read();    sort(p,p+n);    m=ConvexHull(p,n,ch);    For(i,0,m-1) {        Point tp=ch[(i+1)%m]-ch[i];        ans+=max(abs(tp.x),abs(tp.y));    }    cout<<ans+4<<endl;}int main(){//    fre("in.txt","r",stdin);    int t=0;    solve();    return 0;}

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[Codeforces50C]Happy Farm 5 凸包