feat(day-6): add part 1 solution

2 files changed, 31 insertions, 0 deletions

diff --git a/day-6/input.txt b/day-6/input.txt
new file mode 100644
index 0000000..e5c8984
--- /dev/null
+++ b/day-6/input.txt
@@ -0,0 +1,2 @@
+Time:        59     70     78     78
+Distance:   430   1218   1213   1276
diff --git a/day-6/script.ts b/day-6/script.ts
new file mode 100644
index 0000000..951e056
--- /dev/null
+++ b/day-6/script.ts
@@ -0,0 +1,29 @@
+import fs from "fs";
+
+const input = fs.readFileSync("./input.txt").toString();
+
+const [times, distances] = input
+  .split("\n")
+  .slice(0, 2)
+  .map((s) => s.match(/\d+/g)?.map(Number) || []);
+
+function numberOfWaysToWin(time: number, record: number) {
+  // Solution to quadratic:
+  // x(time-x) > record
+  // on the domain [0, time]
+  const sqrt = Math.sqrt(time * time - 4 * record);
+  const [min, max] = [-1, +1].map((sign) => 0.5 * (time + sqrt * sign));
+
+  const wholeMin = Math.floor(min) + 1;
+  const wholeMax = Math.ceil(max);
+  return wholeMax - wholeMin;
+}
+
+const result = times
+  .map((time, index) => {
+    const distance = distances[index];
+    return numberOfWaysToWin(time, distance);
+  })
+  .reduce((acc, v) => acc * v, 1);
+
+console.log(result);