Area POJ

Area

 POJ - 1654

题意：就是让你求多边形面积

思路：利用多边形面积公式即可，输出格式第一次见。。。wa了好几发。。

// 
// Created by HJYL on 2020/2/3.
//
#include<iostream>
#include<cstring>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;
const double eps=1e-8;
const int maxn=1e6+5;
struct Point{
    int x,y;
    Point(int x=0,int y=0):x(x),y(y){}
    Point operator - (Point const &b)const
    {
        return Point(x-b.x ,y-b.y);
    }
    bool operator < (Point const &c)const{
        if(x==c.x)
            return y<c.y;
        return x<c.x;
    }
}p[maxn];
double Cross(Point A,Point B)
{
    return (A.x*B.y)-(A.y*B.x);
}
long long PolygonArea(Point* p, int n) {//p为端点集合，n为端点个数
    long long s = 0;
    for (int i = 1; i < n - 1; ++i)
        s += Cross(p[i] - p[0], p[i + 1] - p[0]);
    return s<0?-s:s;
}
char s[maxn];
const int dx[]={0,-1,0,1,-1,0,1,-1,0,1};
const int dy[]={0,-1,-1,-1,0,0,0,1,1,1};
int n;
int main()
{
    while(~scanf("%d",&n))
    {
        while(n--)
        {
            getchar();
            scanf("%s",s);
            int l=strlen(s);
            p[0].x=0,p[0].y=0;
            for(int i=1;i<l;i++) {
                p[i].x = p[i - 1].x +dx[s[i]-'0'], p[i].y = p[i - 1].y +dy[s[i]-'0'];
            }
            long long ss=PolygonArea(p,l);
            if(ss%2==0) printf("%lld
",ss/2);
            else printf("%lld.5
",ss/2);
        }
    }
    return 0;
}