BZOJ 1670: [Usaco2006 Oct]Building the Moat护城河的挖掘|二维凸包

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纠结之后还是写的水平序的凸包

极点序也不好写可能有隐含错误

凸包裸题

#include <cmath>#include <queue>#include <ctime>#include <cstdio>#include <cstdlib>#include <cstring>#include <iostream>#include <algorithm>#define LL long long#define ULL unsigned long longconst int mo=1e9+7;const int MAXN=5e3+10;const int MAXM=1e6+10;using namespace std;struct P{int x,y;}num[MAXN];bool cmp(P a,P b){if(a.x==b.x) return a.y<b.y;return a.x<b.x;}int q[MAXN],top;bool b[MAXN];int ff(int x1,int y1,int x2,int y2){return x1*y2-y1*x2;}int f(int z,int y,int x){return ff(num[y].x-num[x].x,num[y].y-num[x].y,num[z].x-num[y].x,num[z].y-num[y].y);}double dis(int x1,int y1,int x2,int y2){return sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));}int main(){int n;scanf("%d",&n);for(int i=1;i<=n;i++) scanf("%d %d",&num[i].x,&num[i].y);sort(num+1,num+n+1,cmp);top=0;for(int i=1;i<=n;i++){while(top>1&&f(i,q[top],q[top-1])>0) top--;q[++top]=i;}for(int i=2;i<=top;i++) b[q[i]]=true;for(int i=n;i>=1;i--) if(!b[i]){while(f(i,q[top],q[top-1])>0) top--;q[++top]=i;}double ans=0;for(int i=2;i<=top;i++) ans+=dis(num[q[i]].x,num[q[i]].y,num[q[i-1]].x,num[q[i-1]].y);printf("%.2lf\n",ans);return 0;}

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