[rust] Grade School

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diff --git a/rust/grade-school/.exercism/metadata.json b/rust/grade-school/.exercism/metadata.json
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+{"track":"rust","exercise":"grade-school","id":"7a8d0123d5884f6d8d1b5e3e6fad84b3","url":"https://exercism.io/my/solutions/7a8d0123d5884f6d8d1b5e3e6fad84b3","handle":"dyamon","is_requester":true,"auto_approve":false}
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diff --git a/rust/grade-school/.gitignore b/rust/grade-school/.gitignore
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+# Generated by Cargo
+# will have compiled files and executables
+/target/
+**/*.rs.bk
+
+# Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
+# More information here http://doc.crates.io/guide.html#cargotoml-vs-cargolock
+Cargo.lock
diff --git a/rust/grade-school/Cargo.toml b/rust/grade-school/Cargo.toml
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+++ b/rust/grade-school/Cargo.toml
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+[package]
+edition = "2018"
+name = "grade-school"
+version = "0.0.0"
diff --git a/rust/grade-school/README.md b/rust/grade-school/README.md
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+# Grade School
+
+Given students' names along with the grade that they are in, create a roster
+for the school.
+
+In the end, you should be able to:
+
+- Add a student's name to the roster for a grade
+  - "Add Jim to grade 2."
+  - "OK."
+- Get a list of all students enrolled in a grade
+  - "Which students are in grade 2?"
+  - "We've only got Jim just now."
+- Get a sorted list of all students in all grades.  Grades should sort
+  as 1, 2, 3, etc., and students within a grade should be sorted
+  alphabetically by name.
+  - "Who all is enrolled in school right now?"
+  - "Let me think. We have
+  Anna, Barb, and Charlie in grade 1,
+  Alex, Peter, and Zoe in grade 2
+  and Jim in grade 5.
+  So the answer is: Anna, Barb, Charlie, Alex, Peter, Zoe and Jim"
+
+Note that all our students only have one name.  (It's a small town, what
+do you want?)
+
+## For bonus points
+
+Did you get the tests passing and the code clean? If you want to, these
+are some additional things you could try:
+
+- If you're working in a language with mutable data structures and your
+  implementation allows outside code to mutate the school's internal DB
+  directly, see if you can prevent this. Feel free to introduce additional
+  tests.
+
+Then please share your thoughts in a comment on the submission. Did this
+experiment make the code better? Worse? Did you learn anything from it?
+
+## Rust Installation
+
+Refer to the [exercism help page][help-page] for Rust installation and learning
+resources.
+
+## Writing the Code
+
+Execute the tests with:
+
+```bash
+$ cargo test
+```
+
+All but the first test have been ignored. After you get the first test to
+pass, open the tests source file which is located in the `tests` directory
+and remove the `#[ignore]` flag from the next test and get the tests to pass
+again. Each separate test is a function with `#[test]` flag above it.
+Continue, until you pass every test.
+
+If you wish to run all ignored tests without editing the tests source file, use:
+
+```bash
+$ cargo test -- --ignored
+```
+
+To run a specific test, for example `some_test`, you can use:
+
+```bash
+$ cargo test some_test
+```
+
+If the specific test is ignored use:
+
+```bash
+$ cargo test some_test -- --ignored
+```
+
+To learn more about Rust tests refer to the [online test documentation][rust-tests]
+
+Make sure to read the [Modules][modules] chapter if you
+haven't already, it will help you with organizing your files.
+
+## Further improvements
+
+After you have solved the exercise, please consider using the additional utilities, described in the [installation guide](https://exercism.io/tracks/rust/installation), to further refine your final solution.
+
+To format your solution, inside the solution directory use
+
+```bash
+cargo fmt
+```
+
+To see, if your solution contains some common ineffective use cases, inside the solution directory use
+
+```bash
+cargo clippy --all-targets
+```
+
+## Submitting the solution
+
+Generally you should submit all files in which you implemented your solution (`src/lib.rs` in most cases). If you are using any external crates, please consider submitting the `Cargo.toml` file. This will make the review process faster and clearer.
+
+## Feedback, Issues, Pull Requests
+
+The [exercism/rust](https://github.com/exercism/rust) repository on GitHub is the home for all of the Rust exercises. If you have feedback about an exercise, or want to help implement new exercises, head over there and create an issue. Members of the rust track team are happy to help!
+
+If you want to know more about Exercism, take a look at the [contribution guide](https://github.com/exercism/docs/blob/master/contributing-to-language-tracks/README.md).
+
+[help-page]: https://exercism.io/tracks/rust/learning
+[modules]: https://doc.rust-lang.org/book/ch07-02-defining-modules-to-control-scope-and-privacy.html
+[cargo]: https://doc.rust-lang.org/book/ch14-00-more-about-cargo.html
+[rust-tests]: https://doc.rust-lang.org/book/ch11-02-running-tests.html
+
+## Source
+
+A pairing session with Phil Battos at gSchool [http://gschool.it](http://gschool.it)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.
diff --git a/rust/grade-school/src/lib.rs b/rust/grade-school/src/lib.rs
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+use std::collections::{BTreeMap, BTreeSet};
+
+#[derive(Default)]
+pub struct School(BTreeMap<u32, BTreeSet<String>>);
+
+impl School {
+    pub fn new() -> School {
+        Self::default()
+    }
+
+    pub fn add(&mut self, grade: u32, student: &str) {
+        self.0.entry(grade).or_default().insert(student.to_string());
+    }
+
+    pub fn grades(&self) -> Vec<u32> {
+        self.0.keys().cloned().collect()
+    }
+
+    pub fn grade(&self, grade: u32) -> Option<Vec<String>> {
+        self.0.get(&grade).map(|vs| vs.iter().cloned().collect())
+    }
+}
diff --git a/rust/grade-school/tests/grade-school.rs b/rust/grade-school/tests/grade-school.rs
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+++ b/rust/grade-school/tests/grade-school.rs
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+use grade_school as school;
+
+fn some_strings(v: &[&str]) -> Option<Vec<String>> {
+    Some(v.iter().map(|s| s.to_string()).collect())
+}
+
+#[test]
+fn test_grades_for_empty_school() {
+    let s = school::School::new();
+    assert_eq!(s.grades(), vec![]);
+}
+
+#[test]
+fn test_grades_for_one_student() {
+    let mut s = school::School::new();
+    s.add(2, "Aimee");
+    assert_eq!(s.grades(), vec![2]);
+}
+
+#[test]
+fn test_grades_for_several_students_are_sorted() {
+    let mut s = school::School::new();
+    s.add(2, "Aimee");
+    s.add(7, "Logan");
+    s.add(4, "Blair");
+    assert_eq!(s.grades(), vec![2, 4, 7]);
+}
+
+#[test]
+fn test_grades_when_several_students_have_the_same_grade() {
+    let mut s = school::School::new();
+    s.add(2, "Aimee");
+    s.add(2, "Logan");
+    s.add(2, "Blair");
+    assert_eq!(s.grades(), vec![2]);
+}
+
+#[test]
+fn test_grade_for_empty_school() {
+    let s = school::School::new();
+    assert_eq!(s.grade(1), None);
+}
+
+#[test]
+fn test_grade_when_no_students_have_that_grade() {
+    let mut s = school::School::new();
+    s.add(7, "Logan");
+    assert_eq!(s.grade(1), None);
+}
+
+#[test]
+fn test_grade_for_one_student() {
+    let mut s = school::School::new();
+    s.add(2, "Aimee");
+    assert_eq!(s.grade(2), some_strings(&["Aimee"]));
+}
+
+#[test]
+fn test_grade_returns_students_sorted_by_name() {
+    let mut s = school::School::new();
+    s.add(2, "James");
+    s.add(2, "Blair");
+    s.add(2, "Paul");
+    assert_eq!(s.grade(2), some_strings(&["Blair", "James", "Paul"]));
+}
+
+#[test]
+fn test_add_students_to_different_grades() {
+    let mut s = school::School::new();
+    s.add(3, "Chelsea");
+    s.add(7, "Logan");
+    assert_eq!(s.grades(), vec![3, 7]);
+    assert_eq!(s.grade(3), some_strings(&["Chelsea"]));
+    assert_eq!(s.grade(7), some_strings(&["Logan"]));
+}