I have been trying to get my feet wet programming in Rust.
A month and a half ago, I thought “Maybe I will hack up an Earley parser in a variety of languages, including Rust.” That sent me down a long path of learning about how Earley parsing works; I have not yet written up my results from that investigation, and I still have not written the Rust version of the code.
Last weekend, I sat down and said, “Let’s try a simpler goal: A couple simple exercies, maybe taken from Knuth’s TAOCP” This was indeed a much simpler goal, but it was more difficult than I had expected.
So, here is a Rust hacking puzzle that I struggled with.
I am representing piles of playing cards via linked structures. Here are the data structure declarations:
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Note that the
next field is an (optional) owned pointer to the
next card in the pile.
Option<~card> will be generally used to
represent a potentially empty pile (or “stack”, “deck” or “hand”, as
the context dictates), while
~card is a non-empty pile (or, when its
None, a single card, again as context dictates)
I want to write four functions:
pop_bot, which respectively:
place_top(stack, c)pushes a card
conto the top of the stack, represented by return the new top of the stack.
place_bot(stack, c)places a card beneath the stack. For an empty stack, the placed card is returned as the top of the newly formed stack; otherwise, the old stack top is returned (since the stack is imperatively modified).
pop_top(stack)pops the top of the stack, returning a tuple of the popped card and the remaining, potentially empty stack.
pop_bot(stack)removes the bottom of the stack (i.e. “deals from the bottom of the deck”), returning a tuple of the removed card and the new, potentially empty stack.
In code, here are the signatures for the desired functions, as well as one-line reminders of the behavior for each.
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(Some non-critical helper infrastructure follows, showing off Rust as language)
Here is some example code that puts together a hand and does a few manipulations using the above operations (as well as some printing routines to make looking at these cards nicer in the terminal output)
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In my terminal, I get the following output from the above
initial hand: 2♦,3♠,10♣
place top: A♦
new hand: A♦,2♦,3♠,10♣
place bot: 6♦
new hand: A♦,2♦,3♠,10♣,6♦
popped top: A♦
new hand: 2♦,3♠,10♣,6♦
popped bot: 6♦
new hand: 2♦,3♠,10♣
(I will post my initial “solution” to the puzzle in a follow-up post; I wanted to share this first because I know my current solution is non-optimal and wanted to see what others had to offer for how to solve this first.)