comptime primes

rust/nth-prime/.exercism/config.json

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+{
+  "authors": [
+    "sacherjj"
+  ],
+  "contributors": [
+    "attilahorvath",
+    "cbzehner",
+    "coriolinus",
+    "cwhakes",
+    "eddyp",
+    "efx",
+    "ErikSchierboom",
+    "imbolc",
+    "lutostag",
+    "nfiles",
+    "petertseng",
+    "rofrol",
+    "stringparser",
+    "xakon",
+    "ZapAnton"
+  ],
+  "files": {
+    "solution": [
+      "src/lib.rs",
+      "Cargo.toml"
+    ],
+    "test": [
+      "tests/nth_prime.rs"
+    ],
+    "example": [
+      ".meta/example.rs"
+    ]
+  },
+  "blurb": "Given a number n, determine what the nth prime is.",
+  "source": "A variation on Problem 7 at Project Euler",
+  "source_url": "https://projecteuler.net/problem=7"
+}

rust/nth-prime/.gitignore

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+/target
+Cargo.lock

rust/nth-prime/Cargo.toml

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+[package]
+name = "nth_prime"
+version = "0.1.0"
+edition = "2024"
+
+# Not all libraries from crates.io are available in Exercism's test runner.
+# The full list of available libraries is here:
+# https://github.com/exercism/rust-test-runner/blob/main/local-registry/Cargo.toml
+[dependencies]

rust/nth-prime/HELP.md

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+# Help
+
+## Running the tests
+
+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 _only ignored_ tests without editing the tests source file, use:
+
+```bash
+$ cargo test -- --ignored
+```
+
+If you are using Rust 1.51 or later, you can run _all_ tests with
+
+```bash
+$ cargo test -- --include-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].
+
+[rust-tests]: https://doc.rust-lang.org/book/ch11-02-running-tests.html
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit src/lib.rs Cargo.toml` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Rust track's documentation](https://exercism.org/docs/tracks/rust)
+- The [Rust track's programming category on the forum](https://forum.exercism.org/c/programming/rust)
+- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+## Rust Installation
+
+Refer to the [exercism help page][help-page] for Rust installation and learning
+resources.
+
+## 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
+
+Head to [the forum](https://forum.exercism.org/c/programming/rust/) and create a post to provide feedback about an exercise or if you want to help implement new exercises.
+Members of the rust track team are happy to help!
+
+The GitHub [track repository][github] is the home for all of the Rust exercises.
+
+If you want to know more about Exercism, take a look at the [contribution guide].
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.
+
+[help-page]: https://exercism.org/tracks/rust/learning
+[github]: https://github.com/exercism/rust
+[contribution guide]: https://exercism.org/docs/community/contributors

rust/nth-prime/README.md

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+# Nth Prime
+
+Welcome to Nth Prime on Exercism's Rust Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Instructions
+
+Given a number n, determine what the nth prime is.
+
+By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.
+
+If your language provides methods in the standard library to deal with prime numbers, pretend they don't exist and implement them yourself.
+
+Remember that while people commonly count with 1-based indexing (i.e. "the 6th prime is 13"), many programming languages, including Rust, use 0-based indexing (i.e. `primes[5] == 13`). Use 0-based indexing for your implementation.
+
+## Source
+
+### Created by
+
+- @sacherjj
+
+### Contributed to by
+
+- @attilahorvath
+- @cbzehner
+- @coriolinus
+- @cwhakes
+- @eddyp
+- @efx
+- @ErikSchierboom
+- @imbolc
+- @lutostag
+- @nfiles
+- @petertseng
+- @rofrol
+- @stringparser
+- @xakon
+- @ZapAnton
+
+### Based on
+
+A variation on Problem 7 at Project Euler - https://projecteuler.net/problem=7

rust/nth-prime/src/lib.rs

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+const PRIME_LEN: usize = 10_010;
+const LIMIT: usize = 106_000;
+
+struct PrimeCache {
+    primes: [u32; PRIME_LEN],
+}
+
+impl PrimeCache {
+    const fn new() -> Self {
+        let mut primes = [0; PRIME_LEN];
+        let mut sieve = [true; LIMIT];
+
+        sieve[0] = false;
+        sieve[1] = false;
+
+        let mut i = 2;
+        while i * i < LIMIT {
+            if sieve[i] {
+                let mut j = i * i;
+                while j < LIMIT {
+                    sieve[j] = false;
+                    j += i;
+                }
+            }
+            i += 1;
+        }
+        let mut num = 0;
+        let mut j = 0;
+        while num < LIMIT && j < PRIME_LEN {
+            if sieve[num] {
+                primes[j] = num as u32;
+                j += 1;
+            }
+            num += 1;
+        }
+        Self { primes }
+    }
+}
+
+static CACHE: PrimeCache = PrimeCache::new();
+
+pub fn nth(n: u32) -> u32 {
+    let nth = n as usize;
+    if nth >= PRIME_LEN {
+        panic!("N more than comptime was calculated");
+    }
+    CACHE.primes[nth]
+}

rust/nth-prime/tests/nth_prime.rs

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+use nth_prime::*;
+
+#[test]
+fn first_prime() {
+    let output = nth(0);
+    let expected = 2;
+    assert_eq!(output, expected);
+}
+
+#[test]
+fn second_prime() {
+    let output = nth(1);
+    let expected = 3;
+    assert_eq!(output, expected);
+}
+
+#[test]
+fn sixth_prime() {
+    let output = nth(5);
+    let expected = 13;
+    assert_eq!(output, expected);
+}
+
+#[test]
+fn big_prime() {
+    let output = nth(10_000);
+    let expected = 104_743;
+    assert_eq!(output, expected);
+}