Hello Rust! #5 - Coding Challenge (Into trait, pattern matching, stack)

Today we will do a quick interview question called "balanced brackets" (I'm hiding a bug in my code, can you find it? ? Answer here: https://github.com/hello-rust/show/pull/31)
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Markers (for navigation):

Straight to the code!: 1:28
Into trait: 2:12
Using a stack for keeping state: 3:13
A hashmap for matching our input: 5:33
unreachable! macro: 7:14
A mysterious bug: 8:07
Adding more tests: 9:05
Wrapping things up: 9:50

Important Links:
* Unreachable macro: https://doc.rust-lang.org/std/macro.unreachable.html
* Into trait: https://doc.rust-lang.org/std/convert/trait.Into.html
* Creating a Rust function that accepts String or &str: https://hermanradtke.com/2015/05/06/creating-a-rust-function-that-accepts-string-or-str.html

Missing something? Find even more information in the show notes:
https://github.com/hello-rust/show/tree/master/episode/5

Licensing
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Keywords: Into trait, Pattern matching, HashMap, Stack, unreachable! macro, coding puzzle, competitive programming

Hello Rust! is a show about the Rust programming language.
My goal is to address beginner and intermediate Rust questions and show that systems programming can be a lot of fun!

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