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c9f66fd425
This is the result of running `dprint fmt` after removing `src/` from
the list of excluded directories.
This also reformats the Rust code: we might want to tweak this a bit in
the future since some of the changes removes the hand-formatting. Of
course, this formatting can be seen as a mis-feature, so maybe this is
good overall.
Thanks to mdbook-i18n-helpers 0.2, the POT file is nearly unchanged
after this, meaning that all existing translations remain valid! A few
messages were changed because of stray whitespace characters:
msgid ""
"Slices always borrow from another object. In this example, `a` has to remain "
-"'alive' (in scope) for at least as long as our slice. "
+"'alive' (in scope) for at least as long as our slice."
msgstr ""
The formatting is enforced in CI and we will have to see how annoying
this is in practice for the many contributors. If it becomes annoying,
we should look into fixing dprint/check#11 so that `dprint` can annotate
the lines that need fixing directly, then I think we can consider more
strict formatting checks.
I added more customization to `rustfmt.toml`. This is to better emulate
the dense style used in the course:
- `max_width = 85` allows lines to take up the full width available in
our code blocks (when taking margins and the line numbers into account).
- `wrap_comments = true` ensures that we don't show very long comments
in the code examples. I edited some comments to shorten them and avoid
unnecessary line breaks — please trim other unnecessarily long comments
when you see them! Remember we're writing code for slides 😄
- `use_small_heuristics = "Max"` allows for things like struct literals
and if-statements to take up the full line width configured above.
The formatting settings apply to all our Rust code right now — I think
we could improve this with https://github.com/dprint/dprint/issues/711
which lets us add per-directory `dprint` configuration files. However,
the `inherit: true` setting is not yet implemented (as far as I can
tell), so a nested configuration file will have to copy most or all of
the top-level file.
121 lines
3.0 KiB
Rust
121 lines
3.0 KiB
Rust
// Copyright 2022 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// ANCHOR: solution
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// This is the buggy version that appears in the problem.
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#[cfg(never)]
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// ANCHOR: luhn
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pub fn luhn(cc_number: &str) -> bool {
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let mut sum = 0;
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let mut double = false;
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for c in cc_number.chars().rev() {
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if let Some(digit) = c.to_digit(10) {
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if double {
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let double_digit = digit * 2;
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sum +=
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if double_digit > 9 { double_digit - 9 } else { double_digit };
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} else {
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sum += digit;
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}
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double = !double;
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} else {
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continue;
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}
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}
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sum % 10 == 0
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}
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// ANCHOR_END: luhn
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// This is the solution and passes all of the tests below.
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pub fn luhn(cc_number: &str) -> bool {
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let mut sum = 0;
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let mut double = false;
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let mut digits = 0;
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for c in cc_number.chars().rev() {
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if let Some(digit) = c.to_digit(10) {
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digits += 1;
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if double {
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let double_digit = digit * 2;
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sum +=
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if double_digit > 9 { double_digit - 9 } else { double_digit };
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} else {
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sum += digit;
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}
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double = !double;
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} else if c.is_whitespace() {
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continue;
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} else {
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return false;
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}
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}
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digits >= 2 && sum % 10 == 0
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}
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fn main() {
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let cc_number = "1234 5678 1234 5670";
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println!(
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"Is {cc_number} a valid credit card number? {}",
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if luhn(cc_number) { "yes" } else { "no" }
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);
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}
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// ANCHOR: unit-tests
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#[cfg(test)]
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mod test {
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use super::*;
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#[test]
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fn test_valid_cc_number() {
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assert!(luhn("4263 9826 4026 9299"));
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assert!(luhn("4539 3195 0343 6467"));
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assert!(luhn("7992 7398 713"));
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}
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#[test]
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fn test_invalid_cc_number() {
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assert!(!luhn("4223 9826 4026 9299"));
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assert!(!luhn("4539 3195 0343 6476"));
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assert!(!luhn("8273 1232 7352 0569"));
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}
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// ANCHOR_END: unit-tests
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#[test]
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fn test_non_digit_cc_number() {
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assert!(!luhn("foo"));
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assert!(!luhn("foo 0 0"));
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}
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#[test]
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fn test_empty_cc_number() {
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assert!(!luhn(""));
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assert!(!luhn(" "));
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assert!(!luhn(" "));
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assert!(!luhn(" "));
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}
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#[test]
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fn test_single_digit_cc_number() {
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assert!(!luhn("0"));
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}
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#[test]
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fn test_two_digit_cc_number() {
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assert!(luhn(" 0 0 "));
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}
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}
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