“借鉴”别人的

8.10/I-Wall/main.cpp

@@ -1,65 +1,81 @@
+//参考别人的 
 #include <iostream>
 #include <cmath>
 #include <cstdio>
 #include <algorithm>
 #include<stack>
 using namespace std;
-const double pi=acos(-1.00),eps = 1e-6;//pi3.14~
-const int N=1001,inf=0x3f3f3f3f;
+const double pi=acos(-1.00),eps = 1e-8;//pi3.14~
+const int N=1005,inf=0x3f3f3f3f;
 double ans=0;
-struct dot{
-    int x,y;
-}d[N];
-stack<int>s;
+int q[N],n;
+struct Point{
+    double x,y;
+    Point () {}//无参的构造函数,及初始化、赋初值 
+    Point (double xx,double yy) :x(xx),y(yy) {}
+    Point friend operator - (Point a,Point b)
+    {
+    	return Point(a.x-b.x,a.y-b.y);
+	}
+	double friend operator ^ (Point a,Point b)
+    {
+    	return a.x*b.y-a.y*b.x;
+	}	
+	bool friend operator < (Point a,Point b)
+	{
+		if(a.y==b.y ) return a.x<b.x;
+		return a.y<b.y;
+	}
+}p[N];
+//stack<int>s;
 int sign(double d)
 {
 	if(fabs(d)<eps) return 0;
 	return d>0? 1:-1;
 }
-double cross(double x1, double y1, double x2, double y2)
+//double cross(double x1, double y1, double x2, double y2)
+//{
+//	return x1 * y2 - x2 * y1;
+//}
+double dist(Point a,Point b)
 {
-	return x1 * y2 - x2 * y1;
+	Point c=a-b;
+	return sqrt(c.x*c.x+c.y*c.y);//CE double 
 }
-double length(int x1,int y1,int x2,int y2)
+bool cmp(Point a,Point b)
 {
-	int x=x1-x2,y=y1-y2;
-	return sqrt((double)x*x+y*y);//CE double 
+	int s=sign((a-p[1])^(b-p[1]));
+	if(s>0||(s==0&&dist(a,p[1])<dist(b,p[1])))return 1;
+	else return 0;
+}
+double Graham()
+{
+	sort(p+1,p+n+1);
+	sort(p+1,p+1+n,cmp);
+	int top=3;
+	q[1]=1,q[2]=2,q[3]=3;
+	for(int i=4;i<=n;i++)
+	{
+		while(top>1&&sign((p[q[top]]-p[q[top-1]])^(p[i]-p[q[top]]))<=0){
+			top--;
+		}
+		q[++top]=i;
+	}
+	double res=0;
+	for(int i=1;i<top;i++)
+	{
+		res+=dist(p[q[i]],p[q[i+1]]);
+	}
+	return res+dist(p[q[1]],p[q[top]]);
 }
 int main()
 {
-	int n,l,minn=1,f,ff,x0,x1,x2,y1,y2,y0;
+	int l,minn=1,f,ff,x0,x1,x2,y1,y2,y0;
     scanf("%d%d",&n,&l);
     for(int i=1;i<=n;i++)
     {
-        scanf("%d%d",&d[i].x,&d[i].y);//&!!!
-        minn=d[i].y<d[minn].y? i:minn;
+        scanf("%lf%lf",&p[i].x,&p[i].y);//&!!!
     }
-	int j=(n+minn-2)%n+1;
-//    s.push(minn%n+1);
-    s.push(minn);
-    s.push(j);
-    ans+=length(d[j].x,d[j].y,d[minn].x,d[minn].y);//漏了初始的边 
-    while(j!=minn)
-    {
-		j=(j+n-2)%n+1;
-        f=s.top();
-        s.pop();
-        ff=s.top();
-        while(0>=sign(cross(d[f].x-d[ff].x,d[f].y-d[ff].y,d[j].x-d[ff].x,d[j].y-d[ff].y)))
-    	{
-    		ans-=length(d[f].x,d[f].y,d[ff].x,d[ff].y);
-//    		printf("--%d(%d,%d),%d(%d,%d): -%lf=%lf\n",f,d[f].x,d[f].y,ff,d[ff].x,d[ff].y,length(d[f].x,d[f].y,d[ff].x,d[ff].y),ans);
-    		f=s.top();
-        	s.pop();
-        	if(s.empty()) break;//RE
-        	ff=s.top();
-		}
-		ans+=length(d[j].x,d[j].y,d[f].x,d[f].y);
-//    	printf("++%d(%d,%d),%d(%d,%d): +%lf=%lf\n",j,d[j].x,d[j].y,f,d[f].x,d[f].y,length(d[j].x,d[j].y,d[f].x,d[f].y),ans);
-		s.push(f);
-		s.push(j);
-	}
-//	printf("%d ",s.size());
-	printf("%.0lf",ans+2*l*pi);//WA*2 （周长跟多边形形状有关）错了，无关，自带四舍五入 
+	printf("%d",(int)(Graham()+pi*2*l+0.5));//(int)()记得加括号 
 	return 0;
 }