README.md

Advent of Befunge

Advent of Code in Befunge

Befunge Summary

Befunge is an esoteric two-dimensional stack language in which the program counter travels around the 80x25 program space. In addition to the stack, program space itself can be modified at runtime.

Instruction	Description
>	Right
<	Left
^	Up
v	Down
?	Random direction
#	Jump over
0 ... 9	Push number
"	Toggle string mode
:	Dup
\	Swap
$	Pop
+	Add
-	Subtract
*	Multiply
/	Divide
%	Modulo
!	Logical NOT
`	Greater than
_	Horizontal if
`	`
g	Get
p	Put
&	Input number
~	Input character
.	Output number
,	Output character
@	Exit
other	In string mode, push character

Development

Solutions run with befrust and debugged with befungee.

Day 1: Not Quite Lisp

Solution

Note: input must not end in a newline.

1. Blue: standard input loop, exiting on EOF (-1).
2. Purple: subtract ASCII value of ) from input, resulting in -1 for ( and 0 for ).
3. Red: add the logical NOT of the result to itself, resulting in -1 for ( and 1 for ).
4. Yellow: subtract the result from the total and output it.

Day 2: I Was Told There Would Be No Math

Solution

1. Blue: standard input loop, exiting on EOF (-1).
2. Purple: check for newline (10).
3. Red: check for "x".
4. Yellow: on "x", discard the input and push 0 for the next number.
5. Green: subtract ASCII value of "0" to convert input to number. Multiply existing number by 10 and add the input number.
6. Cyan: on newline, the length, width and height will be on the stack. Replace each "l", "w", "h" in the pink and orange regions with their values.
7. Pink: find the smallest side by calculating each and performing greater-than comparisons.
8. Orange: calculate the areas of each side, add them, and multiply by two. Add the area of the smallest side. Add the area to the total, output, then push 0 for the next input value.

Day 3: Perfectly Spherical Houses in a Vacuum

Solution

Note: non-standard Befunge, 255x255 program space.

1. Blue: push starting coordinates (128, 128), the center of a 255x255 program space.
2. Purple: temporarily store coordinates under blue region, use them to write a 1 into the program space, then restore the coordinates to the stack.
3. Red: input loop checking for newline (10).
4. Yellow: compare input to "<", leaving the difference on the stack.
5. Green: compare input to 2, the difference between "<" and ">", again leaving the difference on the stack.
6. Cyan: compare input to 32, the difference between ">" and "^", again leaving the difference on the stack. It is assumed that any other value is "v".
7. Pink: pop input value and add or subtract 1 to the X or Y coordinate.
8. Orange: pop input and coordinates to empty the stack and enter the gray area.
9. Gray: region of program space populated with 1 instructions by the input loop, then executed.
10. Lime: sum the entire stack full of 1s, output the result and exit.

Map of the houses Santa visited in program space:

Day 4: The Ideal Stocking Stuffer

No solution yet.

Day 5: Doesn't He Have Intern-Elves For This?

No solution yet.