Selection Sorting Using 2 Arrays - c++

Question

Suppose I want to take an array of pointers that point to x, y, z coordinates such as:
(1, 2, 4)
(2, 3, 8)
(3, 5, 1)
Then I wanted to take each of those values and compare the distance from point (1, 2, 3) and then sort the distance from each point in descending order.
How would I do that? This is the code I have so far. But I dont know how to get the second array to point back to the original values. Any help would be great.
void sortPointsByDistanceFromRefPoint(Points* points, Point* ref_point)
{
double *array;
double x0,y0,z0;
x0 =ref_point->x;
y0 =ref_point->y;
z0 =ref_point->z;
Point** point_array = points-> point_array;
int num_points = points->num_points;
array = new double[num_points];
double distance;
double x,y,z;
for (int i = 0; i< num_points; i++)
{
Point* point = point_array[i];
x = point->x;
y = point ->y;
z = point ->z;
distance = sqrt( pow((x-x0),2) + pow((y- y0),2) + pow((z-z0),2));
array[i] = distance;
}
double tmp;
for( int i = 0; i < num_points; i++)
cout << array[i] << " " << endl;
cout << endl;
cout << endl;
for (int i = 0; i < num_points -1; i++)
for (int j = i+1; j < num_points; j++)
if (array[i] > array[j])
{
tmp = array[i];
array[i] = array[j];
array[j] = tmp;
}
for( int i = 0; i < num_points; i++)
cout << array[i] << " " << endl;
cout << endl;
delete [] array;
}

Answer 1

When you swap the values in array using
tmp = array[i];
array[i] = array[j];
array[j] = tmp;
also swap the values(pointers) in point_array:
Point* tmpPoint = point_array[i];
point_array[i] = point_array[j];
point_array[j] = tmpPoint;

Answer 2

First you need to iterate over both arrays at the same time and calculate their distances. As you calculated their distances you can add them to a list, or another array. But while you are adding the distances to the list, add them in sorted order. You can have a method AddDistance(double distance). The first incoming distance goes into the sorted array as the first element. Then when the next one comes, you check it's value and compare it to all the other elements in the array. Here is pseudo code that can do the job for you:
double sortedDistances[100];
int sortedDistancesSize;
void InsertDistance(double distance)
{
int i=0;
for(i=0; i < sortedDistancesSize, sortedDistances[i] < distance; ++i);
InsertNewDistance(distance, i);
}
Your InsertNewDistance method should insert the given distance at position "i" and shift the contents of the array after position "i" to the right.