题目链接：http://acm.hdu.edu.cn/showPRoblem.php?pid=1392 题意:给你n棵树，让你用一根绳子把全部树围起来，要绳子尽可能的短，其实也就是求凸包的周长 解析：凸包裸题，然而我莫名其妙调了两个钟的bug，我还是太菜了
#include <cmath>#include <algorithm>#include <iostream>#include <cstdio>#include <vector>#include <cstring>#include <stack>using namespace std;const int maxn = 1000000+10;const double eps = 1e-5;struct point{ double x; double y; point() {} point(double _x,double _y) { x = _x; y = _y; } bool Operator < (const point b)const { if(y==b.y) return x<b.x; return y<b.y; }}a[maxn],ans[maxn];double x_mul(point p0,point p1,point p2){ return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);}double dis(point a,point b){ return sqrt(1.0*(a.x-b.x)*(a.x-b.x)+1.0*(a.y-b.y)*(a.y-b.y));}//极角排序int cmp(point t1,point t2){ double tmp=x_mul(a[0],t1,t2); if(tmp==0) return dis(a[0],t1)<dis(a[0],t2); return tmp>0;}double graham(int n){ sort(a,a+n); sort(a+1,a+n,cmp); ans[0] = a[0]; ans[1] = a[1]; ans[2] = a[2]; int top = 2; for(int i=3;i<n;i++) { while(top>=2&&x_mul(ans[top-1],ans[top],a[i])<0) top--; ans[++top] = a[i]; } double res = 0; for(int i=0;i<top;i++) { //printf("%.2f %.2f/n",ans[i].x,ans[i].y); res += dis(ans[i],ans[i+1]); } //printf("%.2f %.2f/n",ans[top].x,ans[top].y); res += dis(ans[top],ans[0]); return res;}int main(void){ int n; while(~scanf("%d",&n)&&n) { for(int i=0;i<n;i++) scanf("%lf %lf",&a[i].x,&a[i].y); if(n==1) { puts("0.0"); continue; } else if(n==2) { printf("%.2f/n",dis(a[0],a[1])); continue; } double ans = graham(n); printf("%.2f/n",ans); } return 0;}新闻热点
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