Day 13

2024/13/index.ts

@@ -0,0 +1,55 @@
+const fs = require('fs');
+
+const input = fs.readFileSync(__dirname + '/input.txt', 'utf8');
+
+const lines = input.split("\n");
+
+interface Coord { x: number, y: number };
+
+interface equation {
+    prize: Coord,
+    a: Coord,
+    b: Coord,
+}
+
+const equations: Array<equation> = [];
+
+for (let i = 0; i < lines.length; i += 4) {
+    let match = lines[i].match(/Button A: X\+(\d+), Y\+(\d+)/);
+    const a = { x: parseInt(match[1]), y: parseInt(match[2]) };
+    match = lines[i + 1].match(/Button B: X\+(\d+), Y\+(\d+)/);
+    const b = { x: parseInt(match[1]), y: parseInt(match[2]) };
+    match = lines[i + 2].match(/Prize: X=(\d+), Y=(\d+)/);
+    const prize = { x: parseInt(match[1]), y: parseInt(match[2]) };
+    // Part 2
+    prize.x += 10000000000000;
+    prize.y += 10000000000000;
+
+    equations.push({ prize, a, b });
+}
+
+let result = 0;
+
+equations.forEach(({ a, b, prize }) => {
+    // x*94 + y*22 = 8400
+    // x*34 + y*67 = 5400
+    // x = (8400 - y*22)/94
+    // ((8400 - y*22)/94)*34 + y*67 = 5400
+    // (8400 - y*22) + ((y*67*94)/34) = 5400 * 94/34
+    // ((y*67*94)/34) - y*22 = ((5400 * 94/34)/34) - 8400
+    // y * (((67*94)/34) - 22) = ((5400 * 94)/34) - 8400
+    // y = (((5400 * 94)/34) - 8400) / (((67*94)/34) - 22)
+
+    const bPresses = (((prize.y * a.x) / a.y) - prize.x) / (((b.y * a.x) / a.y) - b.x);
+    const aPresses = (prize.x - (bPresses * b.x)) / a.x;
+
+    if (
+        Math.abs(bPresses - Math.round(bPresses)) < 0.001
+        && Math.abs(aPresses - Math.round(aPresses)) < 0.001
+        && aPresses > 0 && bPresses > 0
+    ) {
+        result += (Math.round(aPresses) * 3) + Math.round(bPresses);
+    }
+});
+
+console.log(result);