The most important functions are listed below:

// Judge if there exist a parabola passing P[a] and P[b]
// The validation of direction of the parabola is included in the positive sign
bool Valid(int a, int b)
{
    if (P[a].x == P[b].x)
        return false;
    else return (P[a].x - P[b].x) * (P[a].x * P[b].y - P[b].x * P[a].y) > 0;
}

// Judge if the parabola passing P[a] and P[b] also passes P[c]
// Using the determinant for judgement
bool Pass(int a, int b, int c)
{
    return (P[a].x * P[a].x) * P[b].x * P[c].y +
        P[a].x * P[b].y * (P[c].x * P[c].x) +
        P[a].y * (P[b].x * P[b].x) * P[c].x -
        (P[a].x * P[a].x) * P[b].y * P[c].x -
        P[a].x * (P[b].x * P[b].x) * P[c].y -
        P[a].y * P[b].x * (P[c].x * P[c].x) == 0;
}

Note: using long integers (64-bit) to avoid overflow.

Good luck.

I've got AC then complete test for a<0 && b!=0:
1 999
2 999
3 0
4 1
5 2
answ 3...
Good Luck!

Edited by author 23.10.2011 01:27

Edited by author 23.10.2011 04:20

What is it? So, in russian vertion of problem x[i]>0, y[i]>0... is it true?
Whether is there any mistake while doing
translation from English to Russian?
Where should I seek an error?

Edited by author 24.01.2017 00:30

Edited by author 24.01.2017 00:30

I passed it, there was an defect in my algo :-)

Edited by author 30.04.2015 23:51

wa on test24 who can help me!= =
what's the data?

I have a problem when comparing real numbers

       private static double EPS = 0.33333333333333;

       public static boolean eq (double a, double b) {
          return Math.abs (a - b) <EPS;
       }

when checking whether a given point belongs to a parabola, I simply substitutes the x and y
the function (y = x ^ 2 * a + x * b)
I can not pass the test 57

Edited by author 18.09.2012 18:13

Edited by author 27.05.2014 23:45

I can't imagine what can it be couse i tried all tests from another topic and also mine but all of my and other's tests it solves, but test #3
Could you help me?

parabola function helps for you !!!
k = x1 * x2 * (x2 - x1);
a = y2 * x1 -  y1 * x2;               // a = (y2 * x1 -  y1 * x2) / k;
b = y1 * x2 * (x2 - x1) - a * x1;     // b = (y1 * x2 * (x2 - x1) - a * x1) / k

if(y[i] * k == a * x[i] * x[i] + b * x[i])   delete index i ...

What is in test №2?

I used eps=0, eps=1e-10,1e-9,1e-8,1e-7, but #45 is wrong with each eps((

may i use 'struct' in my programm?

Edited by author 25.10.2011 21:34