zoj 1465 || poj 1113 Wall

看论文的时候看到的题，给你一个多边形，需要用最少的离这个多边形远为L的墙围住。凸包的话是距离最短的。画图的话，可知，拐角部分都是圆弧，整个一周下来正好是半径为L的圆的周长。所以结果就是凸包周长+圆周长。

 

我发现死活过不去，然后看人家的排序，我没有判断距离，改了改，居然过了><。。。难道我以前写的凸包排序都是错的？？！！、、、好恐怖。。。记住了。。

 

#include <queue>#include <stack>#include <math.h>#include <stdio.h>#include <stdlib.h>#include <iostream>#include <limits.h>#include <string.h>#include <algorithm>using namespace std;const int MAX = 1010;const double eps = 1e-10;const double pi = acos(-1.0);typedef struct Point{double x,y;}Point;Point c[MAX];bool dy(double x,double y) // x > y {return x > y + eps;}bool xy(double x,double y) // x < y {return x < y - eps;}bool dyd(double x,double y) // x >= y {return x > y - eps;}bool xyd(double x,double y) // x <= y {return x < y + eps;}bool dd(double x,double y) // x == y {return fabs( x - y ) < eps;}double crossProduct(Point a,Point b,Point c)//向量 ac 在 ab 的方向 {return (c.x - a.x)*(b.y - a.y) - (b.x - a.x)*(c.y - a.y);}double Distance(Point a,Point b) // a b 两点之间的距离 {return sqrt( ( a.x - b.x ) * ( a.x - b.x ) + ( a.y - b.y ) * ( a.y - b.y ) );}bool cmp(Point a,Point b) // 第一次排序 {if( dd(a.y ,b.y ) )return xy(a.x, b.x);return xy(a.y,b.y);}bool cmp1(Point a,Point b) // 第二次排序 {double len = crossProduct(c[0],a,b);if( dd(len,0.0) )return xy(Distance(c[0],a),Distance(c[0],b));return xy(len,0.0);}double circum(double r){return 2 * pi * r;}Point stk[MAX];int top;double dis(){double sum = 0.0;for(int i=0; i<top; i++)sum += Distance(stk[i],stk[i+1]);sum += Distance(stk[0],stk[top]);return sum;}double Graham(int n){sort(c,c+n,cmp);sort(c+1,c+n,cmp1);top = 0;stk[top++] = c[0];stk[top++] = c[1];stk[top++] = c[2];top--;for(int i=3; i<n; i++){while(1){Point a,b;a = stk[top];b = stk[top-1];if( xyd( crossProduct(a,b,c[i]), 0.0 ) )top--;elsebreak;}stk[++top] = c[i];}return dis();}int main(){int ncases;int n,l;scanf("%d",&ncases);while( ncases-- ){scanf("%d %d",&n,&l);for(int i=0; i<n; i++)scanf("%lf %lf",&c[i].x,&c[i].y);double ans = Graham(n);double len = circum(l);printf("%.0lf/n",(ans+len));if( ncases )printf("/n");} return 0;}