feature: Squares With Three Sides

Author: mariotacke

README.md

@@ -8,6 +8,7 @@ Collect stars by solving puzzles. Two puzzles will be made available on each day
 
 - [Day 1: No Time for a Taxicab](day-01-no-time-for-a-taxicab/)
 - [Day 2: Bathroom Security](day-02-bathroom-security/)
+- [Day 3: Squares With Three Sides](day-03-squares-with-three-sides/)
 
 ## Running Tests
 

day-03-squares-with-three-sides/README.md

@@ -0,0 +1,14 @@
+# Day 3: Squares With Three Sides
+
+Now that you can think clearly, you move deeper into the labyrinth of hallways and office furniture that makes up this part of Easter Bunny HQ. This must be a graphic design department; the walls are covered in specifications for triangles.
+
+Or are they?
+
+The design document gives the side lengths of each triangle it describes, but... `5 10 25`? Some of these aren't triangles. You can't help but mark the impossible ones.
+
+In a valid triangle, the sum of any two sides must be larger than the remaining side. For example, the "triangle" given above is impossible, because `5 + 10` is not larger than `25`.
+
+In your puzzle input, **how many** of the listed triangles are **possible**?
+
+## References
+- https://adventofcode.com/2016/day/3

day-03-squares-with-three-sides/test.js

@@ -0,0 +1,18 @@
+const assert = require('assert');
+
+const { isPossibleTriangle, countValidTriangles } = require('./triangle');
+
+describe('Day 3: Squares With Three Sides', () => {
+  it('should determine if triangle is possible', () => {
+    assert.strictEqual(isPossibleTriangle(5, 10, 25), false);
+    assert.strictEqual(isPossibleTriangle(3, 4, 6), true);
+  });
+
+  it('should count valid triangles', () => {
+    const list =
+      `5 10 25
+       3 4 6`;
+
+    assert.strictEqual(countValidTriangles(list), 1);
+  });
+});

day-03-squares-with-three-sides/triangle.js

@@ -0,0 +1,28 @@
+const isPossibleTriangle = (a, b, c) => a + b > c;
+
+const countValidTriangles = (input) => {
+  return input
+    .split('\n')
+    .map((row) => {
+      const sides = row
+        .trim()
+        .split(' ')
+        .filter((x) => x.length)
+        .map((x) => parseInt(x))
+        .sort((a, b) => a - b);
+
+      return {
+        a: sides[0],
+        b: sides[1],
+        c: sides[2],
+      };
+    })
+    .map(({ a, b, c }) => isPossibleTriangle(a, b, c))
+    .filter((t) => t)
+    .length;
+};
+
+module.exports = {
+  isPossibleTriangle,
+  countValidTriangles,
+};