pku 1654 Area(向量叉积算面积)

经典问题，求多边形面积，用向量叉积可以很好的解决。

#include <iostream>using namespace std;int move[10][2]={{0,0},{-1,-1},{0,-1},{1,-1},{-1,0},{0,0},{1,0},{-1,1},{0,1},{1,1}};int main(){int n;__int64 ans;int x1,y1,x2,y2;char next;scanf("%d",&n);while(n--){ans=0;x1=y1=0;while(scanf("%c",&next)&&next!='5'){x2=x1+move[next-'0'][0];y2=y1+move[next-'0'][1];ans+=x1*y2-y1*x2;x1=x2;y1=y2;}if(ans<0) ans=-ans;if(ans%2) printf("%.1f/n",((double)ans)/2);else printf("%I64d/n",ans/2);}return 0;}