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Problem B
Befunge
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Befunge is a two-dimensional, stack-based, self-modifying programming language, described as a cross between Forth and Lemmings. It was created in 1993 by Chris Pressey. A Befunge program is written on a $25\times 80$ torus of characters; control flow is choreographed by following arrow-like symbols. There is a single stack of integers; popping from an empty stack returns the integer $0$.
The instructions are:
|
Digit |
0–9 |
Push this (one-digit) number onto the stack. |
|
Binary operator |
+-*/% |
Pop $a$ and $b$, then push $b\oplus a$. |
|
Negation |
! |
Pop $a$. If $a=0$ then push $1$ else $0$. |
|
Greater than |
‘ |
Pop $a$ and $b$. If $b>a$ then push $1$ else $0$. |
|
Arrows |
<>^v |
Set the direction to left, right, up, down. |
|
Horizontal select |
_ |
Pop $a$; set the direction to right if $a=0$, else left. |
|
Vertical select |
| |
Pop $a$; set the direction to down if $a=0$, else up. |
|
String mode |
" |
Push the following characters’ ASCII value until the next " |
|
Duplicate |
: |
Pop $a$, push $a$ twice. |
|
Put |
p |
Pop $r$, $c$, and $v$. Put $v$ at row $r$, column $c$. |
|
Get |
g |
Pop $r$ and $c$. Push the value at row $r$, column $c$. |
|
Swap |
\ |
Swap two values on top of the stack. |
|
Discard |
$ |
Pop (and discard the result.) |
|
Print number |
. |
Pop $a$ and output $a$ as an integer followed by a space. |
|
Print character |
, |
Pop $a$ and output the $a$th ASCII character. |
|
Bridge |
# |
Skip next cell. |
|
End |
@ |
End program. |
|
Pass |
(Space.) Does nothing. |
Control begins at the leftmost character of the first line of code and proceeds to the right.
For $b$/$a$ and $b$%$a$ you can assume $b\geq 0$ and $a>0$. Division is integer division, rounded down. For put and get, you can assume $0\leq r\leq 24$ and $0\leq c\leq 79$. No arithmetic operation produces a number outside of the range $-2\, 147\, 483\, 648$ to $2\, 147\, 483\, 647$. Every character output by , is a printable character in the ASCII range $20$–$126$ or the newline character with ASCII code $10$. It is guaranteed that the program runs for at most $1\, 000\, 000$ steps and produces at least one non-whitespace symbol.
Input
-
One line with the number $n\in \{ 1,\ldots , 25\} $ of Befunge code lines.
-
$n$ lines of Befunge code, each containing at most $80$ characters.
Output
The output of the Befunge program.
| Sample Input 1 | Sample Output 1 |
|---|---|
1 67*.@ |
42 |
| Sample Input 2 | Sample Output 2 |
|---|---|
5 > v v ,,,,,"Hello"< >48*, v v,,,,,,"World!"< >25*,@ |
Hello World! |
| Sample Input 3 | Sample Output 3 |
|---|---|
3
>25*"!dlroW olleH":v
v:,_@
> ^
|
Hello World! |
| Sample Input 4 | Sample Output 4 |
|---|---|
2 #v> # >19+"sreehC",,,,,,,@ Unreachable code is comments. Note bridge in cell (0, 80). |
Cheers |
| Sample Input 5 | Sample Output 5 |
|---|---|
3 v>25*"sreehC",,,,,,,@ 1>|> # >^ Lines are 80 wide |
Cheers |
| Sample Input 6 | Sample Output 6 |
|---|---|
1 05-. 12/. 67*. 67*, 83%. "x". ")-"87*2+,,, " ", 1\.. 1:.. 10$. 0!. @ |
-5 0 42 *2 120 :-) 0 1 1 1 1 1 |
| Sample Input 7 | Sample Output 7 |
|---|---|
1 "B"70p"A",25*,@ |
B |
| Sample Input 8 | Sample Output 8 |
|---|---|
6 ^v3:-1$$_,#! #:<\*52",Take one down, pass it around,"*520 < ^ >0"elttob erom oN">:#,_$"s"\1-#v_$>0"reeb fo ">:#,_$:2-!| >>\:!#^_:.>0"elttob" ^ >, ^ ^1:_@#:,,,".":<_v#!-3\*25$_,#! #:<" on the wall"0 < ^2:,,"," < <v1:*9+29 |
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