Electric Fences_usaco3.4_皮克定理
2016-10-16 21:04
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Description
给定两个整点(m,n)和(p,0),与坐标原点(0,0)构成三角形,求三角形内的整点数量Analysis
找到这么一道神奇的题目以及神奇的定理皮克定理
一个计算点阵中顶点在格点上的多边形面积公式:S=a+b2−1,其中a表示多边形内部的点数,b表示多边形边界上的点数,s表示多边形的面积
S=ah2,b=p+gcd(n,m)+gcd(|p−n|,m),那么a=S−b2+1
Code
/* ID:wjp13241 PROG:fence9 LANG:C++ */ #include <stdio.h> #include <cmath> using namespace std; struct pos{int x,y;}t[3]; double cros(pos a,pos b,pos c) { return ((a.x-c.x)*(b.y-c.y)-(b.x-c.x)*(a.y-c.y))*0.5; } int gcd(int x,int y) { return !y?x:gcd(y,x%y); } int main() { scanf("%d%d%d",&t[1].x,&t[1].y,&t[2].x); double S=fabs(cros(t[1],t[2],t[0])); int b=t[2].x+gcd(t[1].x,t[1].y)+gcd(fabs(t[2].x-t[1].x),t[1].y); printf("%d\n",(int)(S-b/2+1)); return 0; }
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