Fourth Point !!

链接：https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=1183

题目：

Given are the (

x;y

) coordinates of the endpoints of two adjacent sides of a parallelogram. Find the

(

x;y

) coordinates of the fourth point.

题意：给出一个平行四边形的相邻两条边，求另一个点的坐标

分析：用数学中的向量和好解决，坑在需要判断相邻两边里三个点哪个是公共点，我的方法比较笨拙。

题解：

#include<iostream>double s[8];void change(){double temp;if(s[0]==s[4]&&s[1]==s[5]){temp=s[0],s[0]=s[2],s[2]=temp;temp=s[1],s[1]=s[3],s[3]=temp;}else if(s[0]==s[6]&&s[1]==s[7]){temp=s[0],s[0]=s[2],s[2]=temp;temp=s[1],s[1]=s[3],s[3]=temp;temp=s[4],s[4]=s[6],s[6]=temp;temp=s[5],s[5]=s[7],s[7]=temp;}else if(s[2]==s[6]&&s[3]==s[7]){temp=s[4],s[4]=s[6],s[6]=temp;temp=s[5],s[5]=s[7],s[7]=temp;}}int main(){//freopen("in.txt","r",stdin);while(~scanf("%lf %lf %lf %lf %lf %lf %lf %lf",s,s+1,s+2,s+3,s+4,s+5,s+6,s+7)){change();double ansx,ansy;ansx=s[6]+(s[0]-s[2]);ansy=s[7]+(s[1]-s[3]);printf("%.3lf %.3lf\n",ansx,ansy);}return 0;}