poj 3348 Cows

水题。

 

求凸包面积，没了><。。。贴模板 = =。。

 

#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 = 10010; const double eps = 1e-6; struct point{ double x,y;}; point p[MAX]; point stk[MAX]; int top; bool dy(double x,double y) { return x > y + eps;} // x > y bool xy(double x,double y) { return x < y - eps;} // x < y bool dyd(double x,double y) { return x > y - eps;} // x >= y bool xyd(double x,double y) { return x < y + eps;} // x <= y bool dd(double x,double y) { return fabs( x - y ) < eps;} // x == y 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 disp2p(point a,point b) { 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(p[0],a,b); if( dd(len,0.0) ) return xy(disp2p(p[0],a),disp2p(p[0],b)); return xy(len,0.0); } double area_polygon(point p[],int n) { double s1 = 0.0,s2 = 0.0; for(int i=0; i<n; i++) { s1 += p[(i+1)%n].y * p[i].x; s2 += p[(i+1)%n].y * p[(i+2)%n].x; } return fabs(s1 - s2)/2.0; } double Graham(point p[],int n) { sort(p,p+n,cmp); sort(p+1,p+n,cmp1); top = 0; stk[top++] = p[0]; stk[top++] = p[1]; stk[top++] = p[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,p[i]), 0.0 ) ) top--; else break; } stk[++top] = p[i]; } return area_polygon(stk,top+1); } int main() { int n; while( ~scanf("%d",&n) ) { for(int i=0; i<n; i++) scanf("%lf %lf",&p[i].x,&p[i].y); double s = Graham(p,n); printf("%.0lf/n",floor(s/50.0)); } return 0; }