Area

http://162.105.81.212/JudgeOnline/problem?id=1654

把n边多边形划分成n-2个三角形再利用叉积计算

MLE了一次，WA了两次，算叉积的时候，正负要保留，直到求出总面积时在取绝对值。

#include <iostream>using namespace std ;struct Point{__int64 x , y ;};__int64 step[10][2] ={{0 , 0} , {-1 , -1} , {0 , -1} , {1 , -1} , {-1 , 0} , {0 , 0} , {1 , 0} , {-1 , 1} , {0 , 1} , {1 , 1}} ;Point pre , cur ;char str[1000010] ;__int64 Multiply (Point p1 , Point p2){return p1.x * p2.y - p1.y * p2.x ;}int main (){__int64 i , T , sum ;scanf ("%I64d" , &T) ;while (T --){scanf ("%s" , str) ;cur.x = 0 , cur.y = 0 ;for (sum = 0 , i = 0 ; str[i] != '5' ; i ++){pre = cur ;cur.x += step[str[i] - '0'][0] , cur.y += step[str[i] - '0'][1] ;sum += Multiply (pre , cur) ;}if (sum < 0)sum *= -1 ;if (sum &1)printf ("%I64d.5/n" , sum >> 1) ;elseprintf ("%I64d/n" , sum >> 1) ;}return 0 ;}