Hoj 2485 Myacm Triangles

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题目：http://acm.hit.edu.cn/hoj/problem/view?id=2485

求给定点组成的三角形的面积最大值。并且三角形内部不能有其他点。

暴力+叉积即可。

#include <iostream>#include <stdio.h>#include <stdlib.h>#include <string.h>#include <math.h>#include <vector>using namespace std;struct Point{    char c;    int x;    int y;};Point p[20];//求面积绝对值double cross(Point O,Point A,Point B){    return fabs((A.x - O.x) *  (B.y - O.y) - (B.x - O.x) * (A.y - O.y))/2;}//o是否在ABC中,在返回truebool judge(Point A,Point B,Point C,Point O){    double area = cross(A,B,C);    double s = 0;    s += cross(O,A,B);    s += cross(O,B,C);    s += cross(O,C,A);    if(fabs(area-s)<=1e-8)    {       return true;    }    else    {        return false;    }}int main(){#ifndef ONLINE_JUDGE    freopen("in.txt","r",stdin);#endif    int n;    while(scanf(" %d",&n)!=EOF && n!=0)    {        double area = 0;        Point maxA,maxB,maxC;        for(int i=1; i<=n; i++)        {            scanf(" %c %d %d",&p[i].c,&p[i].x,&p[i].y);        }        for(int i=1; i<=n; i++)        {            for(int j=i+1; j<=n; j++)            {                for(int k=j+1; k<=n; k++)                {                    int flag = 0;                    for(int t=1; t<=n; t++)                    {                        if(t == i || t == j || t == k)                        {                            continue;                        }                        if(judge(p[i],p[j],p[k],p[t]))                        {                            flag = 1;                            break;                        }                    }                    //满足条件的三角形                    if(flag == 0)                    {                        double temp = cross(p[i],p[j],p[k]);                        if(temp > area)                        {                            area = temp;                            maxA = p[i];                            maxB = p[j];                            maxC = p[k];                        }                    }                }            }        }        printf("%c%c%c\n",maxA.c,maxB.c,maxC.c);    }    return 0;}