Question

I have a list of objects that have coordinates. The object is something like this:

private class Seats
{
    public string Code { get; set; }
    public long PosX { get; set; }
    public long PosY { get; set; }
}

For all Seats inside the list, I need to know that they are in group of 4, in a horizontal row. For example, the list below is fine:

List<Seats> good = new List<Seats> {
    new Seats {Code = "A1", PosX = 0, PosY = 0},
    new Seats {Code = "A2", PosX = 1, PosY = 0},
    new Seats {Code = "A3", PosX = 2, PosY = 0},
    new Seats {Code = "A4", PosX = 3, PosY = 0}
};

The list below is also OK (two rows):

List<Seats> good = new List<Seats> {
    new Seats {Code = "A1", PosX = 0, PosY = 0},
    new Seats {Code = "A2", PosX = 1, PosY = 0},
    new Seats {Code = "A3", PosX = 2, PosY = 0},
    new Seats {Code = "A4", PosX = 3, PosY = 0},
    new Seats {Code = "B1", PosX = 0, PosY = 1},
    new Seats {Code = "B2", PosX = 1, PosY = 1},
    new Seats {Code = "B3", PosX = 2, PosY = 1},
    new Seats {Code = "B4", PosX = 3, PosY = 1}
};

The list below is also OK (same row, two groups, gap at (4,0)):

List<Seats> good = new List<Seats> {
    new Seats {Code = "A1", PosX = 0, PosY = 0},
    new Seats {Code = "A2", PosX = 1, PosY = 0},
    new Seats {Code = "A3", PosX = 2, PosY = 0},
    new Seats {Code = "A4", PosX = 3, PosY = 0},
    new Seats {Code = "A6", PosX = 5, PosY = 0},
    new Seats {Code = "A7", PosX = 6, PosY = 0},
    new Seats {Code = "A8", PosX = 7, PosY = 0},
    new Seats {Code = "A9", PosX = 8, PosY = 0}
};

But the list below is not OK because there is a gap at (3,0):

List<Seats> bad1 = new List<Seats> {
    new Seats {Code = "A1", PosX = 0, PosY = 0},
    new Seats {Code = "A2", PosX = 1, PosY = 0},
    new Seats {Code = "A3", PosX = 2, PosY = 0},
    new Seats {Code = "A5", PosX = 4, PosY = 0}
};

The list below is also not OK because there are five of them:

List<Seats> bad2 = new List<Seats> {
    new Seats {Code = "A1", PosX = 0, PosY = 0},
    new Seats {Code = "A2", PosX = 1, PosY = 0},
    new Seats {Code = "A3", PosX = 2, PosY = 0},
    new Seats {Code = "A4", PosX = 3, PosY = 0},
    new Seats {Code = "A5", PosX = 4, PosY = 0}
};

The list below is also not OK because the four Seats need to be in a horizontal row:

List<Seats> bad3 = new List<Seats> {
    new Seats {Code = "A1", PosX = 0, PosY = 0},
    new Seats {Code = "A2", PosX = 1, PosY = 0},
    new Seats {Code = "B1", PosX = 0, PosY = 1},
    new Seats {Code = "B2", PosX = 1, PosY = 1}
};

For checking multiplication of 4 (it can be 8, 12, …) I can just do:

list.Count % 4 == 0

But I need help in how to check ‘in a row’.

Answer 1

Split all values in lists per Y value.

Then for each split list:

• Check that all Y values are equal.
• For X values: Iterate through the list, and check if the difference with the previous is equal the the previous and before previous (check if items exist).

Assuming the points are in order (as in your example), at least for X coordinate.