HDU
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问题描述:
I'm sure this problem will fit you as long as you didn't sleep in your High School Math classes.
Yes,it just need a little math knowledge and I know girls are always smarter than we expeted.
So don't hesitate any more,come and AC it!
Tell you three point A,B,C in a 2-D plain,then a line L with a slope K pass through C,you are going to find
a point P on L,that makes |AP| + |PB| minimal.
Input
The first line contain a t.
Then t cases followed,each case has two parts,the first part is a real number K,indicating the slope,and the second
part are three pairs of integers Ax,Ay,Bx,By,Cx,Cy(0 <=|Ax|,|Ay|,|Bx|,|By|,|Cx|,|Cy| <= 10000 ).
Output
Just out put the minimal |AP| + |PB|(accurate to two places of decimals ).
Sample Input
12.558467 6334 6500 9169 5724 1478Sample Output
3450.55
问题描述:题目给我们一个斜率K,三个点(A,B,C)的坐标,让我们在一条直线(斜率为K,过C点),找到一点P使得|AP|+|BP|最小。
题目分析:我们先求出直线L的方程,然后根据直线方程来判断A与B是否同侧(判断方法就是:将点A,B代入直线方程中算它们的结果的积如果小于0,异测,等于0,至少有一点在直线上,大于0,同侧,判断原理就是:点在直线上方结果大于0,下方小于0,中等于0);
如果异侧:则直接求A与B的距离
如果同侧:则求出A点(B点也可)关于直线L对称的点D,求出B与D 的距离。(求D点时,可以先求出B与D的中点mid(联立方程即可))
代码如下:
#include<iostream>#include<cstdio>#include<cmath>#include<cstring>using namespace std;struct Point{ double x,y;};double get_dis(Point a,Point b){ return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));}int main(){ int t; scanf("%d",&t); while (t--) { double k; Point a,b,c; scanf("%lf",&k); scanf("%lf%lf%lf%lf%lf%lf",&a.x,&a.y,&b.x,&b.y,&c.x,&c.y); double A=k*a.x+c.y-k*c.x-a.y; double B=k*b.x+c.y-k*c.x-b.y; if (A*B<=0) { printf("%.2f\n",get_dis(a,b)); } else { if (k==0) {//当k等于0的时候,中点公式 Point d; d.x=a.x; d.y=2*c.y-a.y; printf("%.2f\n",get_dis(b,d)); } else { double k1,k2,b1,b2; Point mid,d; k1=k,k2=-1.0/k; b1=c.y-k*c.x; b2=a.y+a.x/k; mid.x=(b2-b1)/(k1-k2);//中点 mid.y=k2*mid.x+b2; d.x=2*mid.x-a.x; d.y=2*mid.y-a.y; printf("%.2f\n",get_dis(b,d)); } } } return 0;}
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