My code

#include <iostream>
#include <math.h>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <string>
#include <cstring>
using namespace std;
int main () {
    #ifndef ONLINE_JUDGE
       freopen ("input.txt", "r", stdin);
       freopen ("output.txt", "w", stdout);
    #endif
    int x, y, x1, y1, x2, y2;
    scanf ("%d%d", &x, &y);                         // x - x1 / x2 - x1 = y - y1 / y2 - y1
    scanf ("%d%d%d%d", &x1, &y1, &x2, &y2);
    double AB = sqrt ((double) (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
    double AO = sqrt ((double) (x - x1) * (x - x1) + (y - y1) * (y - y1));
    double OB = sqrt ((double) (x - x2) * (x - x2) + (y - y2) * (y - y2));
//    cout << AB << " " << AO << " " << OB << "\n";
    if (! (round (AO) + round (OB) == round (AB)))
    {
        printf ("NO");
        exit (0);
    }
//    cout << "ok";
    if (y2 - y1 == 0 && x2 - x1 == 0 || x - x1 == 0 || y - y1 == 0)
    {
        printf ("YES");
        exit (0);
    }
    else if (! (y2 - y1 == 0 && x2 - x1 == 0) && (x2 - x1 == 0 || y2 - y1 == 0))
    {
        printf ("NO");
        exit (0);
    }
//    cout << "ok";
    double a = (x - x1) / (x2 - x1);
    double b = (y - y1) / (y2 - y1);
//    cout << a << " " << b << "\n";
    if (a == b)
        printf ("YES");
    else printf ("NO");
return 0;
}