Implement difference-of-squares in zig

zig/difference-of-squares/HELP.md

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+# Help
+
+## Running the tests
+
+Write your code in `<exercise_name>.zig`.
+
+To run the tests for an exercise, run:
+
+```bash
+zig test test_exercise_name.zig
+```
+
+in the exercise's root directory (replacing `exercise_name` with the name of the exercise).
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit difference_of_squares.zig` 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 [Zig track's documentation](https://exercism.org/docs/tracks/zig)
+- The [Zig track's programming category on the forum](https://forum.exercism.org/c/programming/zig)
+- [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.
+
+- [The Zig Programming Language Documentation][documentation] is a great overview of all of the language features that Zig provides to those who use it.
+- [Zig Learn][zig-learn] is an excellent primer that explains the language features that Zig has to offer.
+- [Ziglings][ziglings] is highly recommended.
+  Learn Zig by fixing tiny broken programs.
+- [The Zig Programming Language Discord][discord-zig] is the main [Discord][discord].
+  It provides a great way to get in touch with the Zig community at large, and get some quick, direct help for any Zig related problem.
+- [#zig][irc] on irc.freenode.net is the main Zig IRC channel.
+- [/r/Zig][reddit] is the main Zig subreddit.
+- [Stack Overflow][stack-overflow] can be used to discover code snippets and solutions to problems that may have already asked and maybe solved by others.
+
+[discord]: https://discordapp.com
+[discord-zig]: https://discord.com/invite/gxsFFjE
+[documentation]: https://ziglang.org/documentation/master
+[irc]: https://webchat.freenode.net/?channels=%23zig
+[reddit]: https://www.reddit.com/r/Zig
+[stack-overflow]: https://stackoverflow.com/questions/tagged/zig
+[zig-learn]: https://ziglearn.org/
+[ziglings]: https://github.com/ratfactor/ziglings

zig/difference-of-squares/README.md

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+# Difference of Squares
+
+Welcome to Difference of Squares on Exercism's Zig Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Instructions
+
+Find the difference between the square of the sum and the sum of the squares of the first N natural numbers.
+
+The square of the sum of the first ten natural numbers is
+(1 + 2 + ... + 10)² = 55² = 3025.
+
+The sum of the squares of the first ten natural numbers is
+1² + 2² + ... + 10² = 385.
+
+Hence the difference between the square of the sum of the first ten natural numbers and the sum of the squares of the first ten natural numbers is 3025 - 385 = 2640.
+
+You are not expected to discover an efficient solution to this yourself from first principles; research is allowed, indeed, encouraged.
+Finding the best algorithm for the problem is a key skill in software engineering.
+
+## Source
+
+### Created by
+
+- @massivelivefun
+
+### Based on
+
+Problem 6 at Project Euler - https://projecteuler.net/problem=6

zig/difference-of-squares/difference_of_squares.zig

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+pub fn squareOfSum(number: usize) usize {
+    var sum: usize = 0;
+    for (1..number + 1) |i| {
+        sum += i;
+    }
+
+    sum = sum * sum;
+
+    return sum;
+}
+
+pub fn sumOfSquares(number: usize) usize {
+    var sum: usize = 0;
+    for (1..number + 1) |i| {
+        sum += i * i;
+    }
+
+    return sum;
+}
+
+pub fn differenceOfSquares(number: usize) usize {
+    return squareOfSum(number) - sumOfSquares(number);
+}

zig/difference-of-squares/test_difference_of_squares.zig

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+const std = @import("std");
+const testing = std.testing;
+
+const difference_of_squares = @import("difference_of_squares.zig");
+
+test "square of sum up to 1" {
+    const expected: usize = 1;
+    const actual = difference_of_squares.squareOfSum(1);
+    try testing.expectEqual(expected, actual);
+}
+
+test "square of sum up to 5" {
+    const expected: usize = 225;
+    const actual = difference_of_squares.squareOfSum(5);
+    try testing.expectEqual(expected, actual);
+}
+
+test "square of sum up to 100" {
+    const expected: usize = 25_502_500;
+    const actual = difference_of_squares.squareOfSum(100);
+    try testing.expectEqual(expected, actual);
+}
+
+test "sum of squares up to 1" {
+    const expected: usize = 1;
+    const actual = difference_of_squares.sumOfSquares(1);
+    try testing.expectEqual(expected, actual);
+}
+
+test "sum of squares up to 5" {
+    const expected: usize = 55;
+    const actual = difference_of_squares.sumOfSquares(5);
+    try testing.expectEqual(expected, actual);
+}
+
+test "sum of squares up to 100" {
+    const expected: usize = 338_350;
+    const actual = difference_of_squares.sumOfSquares(100);
+    try testing.expectEqual(expected, actual);
+}
+
+test "difference of squares up to 1" {
+    const expected: usize = 0;
+    const actual = difference_of_squares.differenceOfSquares(1);
+    try testing.expectEqual(expected, actual);
+}
+
+test "difference of squares up to 5" {
+    const expected: usize = 170;
+    const actual = difference_of_squares.differenceOfSquares(5);
+    try testing.expectEqual(expected, actual);
+}
+
+test "difference of squares up to 100" {
+    const expected: usize = 25_164_150;
+    const actual = difference_of_squares.differenceOfSquares(100);
+    try testing.expectEqual(expected, actual);
+}