# Draw Recamán's sequence with ASCII

Recamán's sequence (A005132) is a mathematical sequence, defined as such:

$$A(n) = \begin{cases}0 & \textrm{if } n = 0 \\ A(n-1) - n & \textrm{if } A(n-1) - n \textrm{ is positive and not already in the sequence} \\ % Seems more readable than %A(n-1) - n & \textrm{if } A(n-1) > n \wedge \not\exists m < n: A(m) = A(n-1)-n \\ A(n-1) + n & \textrm{otherwise} \end{cases}$$

An alternative, simpler verbal explanation is as follows:

Subtract unless you can't (the number is negative, or has been used before), in which case add.

The first few terms are $$\0, 1, 3, 6, 2, 7, 13, 20, 12, 21, 11\$$

Now, there is already this challenge which asks you to generate the nth term of the sequence. This one is slightly different.

# Challenge

Given a number n, draw the first n terms of the sequence. What do I mean by 'draw'? Let me demonstrate:

1. Draw a number line max([A(y) for y<=n]) units long. We'll assume n is 5, for now, so the number line is 6 units long (since the largest of $$\A(1) = 0\$$, $$\A(2) = 1\$$, $$\A(3) = 3\$$, $$\A(4) = 6\$$ and $$\A(5) = 2\$$ is $$\6\$$). Make the line from underscores, starting at 0:

______

1. Start with the transition between the first and second terms: that is, 0 and 1. Use | and - to draw a square (equal length and height), going upwards. In this case, we'll have to miss out the - because the distance is only 1.
||
______

1. Now, we'll draw on the next step ($$\A(2) = 1\$$ to $$\A(3) = 3\$$) on the bottom of the line (we alternate between up and down each time):
||
______
| |
|-|


As you can see, this line also has a height of 2, since the height must be equal to the distance between the two terms.

If we continue, we will eventually get to:

   |--|
|  |
|| |  |
______
|||  |
|||  |
|   |
|---|


# Rules

• If there is a - and | colliding, the later one takes priority.
• There may be preceeding/trailing spaces before/after the image, but trailing/preceeding _s or -s are not allowed (exception is 0- or 1- indexing)
• You can choose to set the 0 point just before the first _ on the number line, or just after it.
• No alternative characters for -, | or _ may be used.
• This is , so shortest answer in bytes wins.

# Test case

Here is another test case, with n=10

            |-------|
||-----||
||     ||
|----|    ||     ||
|    |    ||     ||
||--||    ||     ||
||  ||    ||     ||
||||  ||    ||     ||
_____________________
|||  ||   |||     ||
|||  ||   |||     ||
|   ||   |||     ||
|---||   |||     ||
|   |||     ||
|---|||     ||
||------||
|--------|

• It is not clear where left edge of square should be placed. – Daniil Tutubalin Jul 18 '19 at 16:55
• @DaniilTutubalin I'm not sure I understand what you mean. – Geza Kerecsenyi Jul 18 '19 at 16:56
• basically, statement only specifies that we need to draw squares (width = height) and that they should alternate between up and down. There are no instructions about squares' size and position. In test case I see that 2 squares may have the same position of left edge. – Daniil Tutubalin Jul 18 '19 at 17:03
• I think As you can see, this line also has a height of 2, since the height must be equal to the distance between the two terms., as well as You can choose to set the 0 point just before the first _ on the number line, or just after it. wrap this up pretty well. – Geza Kerecsenyi Jul 18 '19 at 17:05
• I think the test case for n=10 is wrong from 13-> 20 onwards. – Nick Kennedy Jul 18 '19 at 21:41

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A full program taking a single integer $$\n\$$ via STDIN and outputting the ASCII art based on zero-indexing.