Very simple in python.

for i in range(int(raw_input())):
    px, py, qx, qy = map(int, raw_input().split())
    print ("{0} {1}".format(2*qx-px, 2*qy-py))

The midPoint formula is the (first coordinate + second coordinate) divided by 2. So for example to find the mid-point between R(2, 2) and P(0, 0) you have to use the formula separately for X and Y. So the middle for X is (Mx = (Rx + Px) / 2 ) and for Y is (My = (Ry + Py) / 2)

Mx = (2 + 0) / 2 = 2 / 2 = 1

My = (2 + 0) / 2 = 2 / 2 = 1

so MidPoint is at coordinates M(1, 1).

What if the MidPoint is given and we have to calculate the point at the other half of the line. Then we use the formula above. So for example if we are given P(0, 0) and the midpoint M(1, 1) you should find R(x, y).

Mx = (Rx + Px) / 2 => Rx = 2Mx - Px

My = (Ry + Py) / 2 => Ry = 2My - Py

And thats how you find the coordinates for R. Here is my code :

#include <iostream>
using namespace std;

int main() {
	
	int n, px, py, mx, my;
	cin >> n;
	
	for (int i = 1; i <= n; i++){
		
		cin >> px >> py >> mx >> my;
		
		int rx = 2 * mx - px;
		int ry = 2 * my - py;
		
		cout << rx << " " << ry << endl;
	}
	
	return 0;
}

Hey guys, I hope you could help me out understanding the problem. From what I understand, the problem is to find the midpoint of a line (or two points). However, I do not understand the output of the given example. How can (2, 2) be the midpoint of (0, 0) and (1, 1)? Shouldn't it be (1/2, 1/2). I guess missing something, but I can't figure it out.

python is bless

for i in range(int(input())):
    x1,y1,x2,y2 = (map(int, input().split()))
    print(x1+(x2-x1)*2, y1+(y2-y1)*2)

What the what??? I cannot use the C# Point class from either System.Drawing or System.Windows. Well shucks!

Its just mid-point formula . [(x_1 + x_2)/2 , (y_1 + y_2)/2]

but instead of finding mid point we have find x2 and y2

import java.io.; import java.util.;

public class Solution {

public static void main(String[] args) {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
    Scanner scan = new Scanner(System.in);
    int test_case = scan.nextInt();
    for(int i=0;i<test_case;i++){
        int x1 = scan.nextInt();
        int y1 = scan.nextInt();
        int x2 = scan.nextInt();
        int y2 = scan.nextInt();

        findNextPoint(x1,x2,y1,y2);
    }
}

private static void findNextPoint(int x1, int x2, int y1, int y2) {
    // TODO Auto-generated method stub
    int x, y;

    x= 2*x2 - x1;
    y = 2*y2 - y1;

    System.out.println(x +" "+y);
}

}

It is basically the mid point formula that we are using.But the problem I have encountered is the test case fails even when the expected output matches with my output.

Minimalistic solution in Swift 4:

for _ in 1...Int(readLine()!)! {
    let line = readLine()!.split(separator:" ").map({Int($0)!})
    print("\(2 * line[2] - line[0]) \(2 * line[3] - line[1])")
}

Minimalistic C# version:

using System.Linq;
using static System.Console;
class Solution {
  static void Main(string[] args) {
    for (int t = int.Parse(ReadLine()); t > 0; t--) {
      var ln = ReadLine().Split(' ').Select(int.Parse).ToArray();
      WriteLine($"{2 * ln[2] - ln[0]} {2 * ln[3] - ln[1]}");
    }
  }
}

C#

        int[] findPoint = new int[2];
        findPoint[0]=(2*qx-px);
        findPoint[1]=(2*qy-py);
        return findPoint;