From 17047ac035b8775936fc26559976ed4d82418bff Mon Sep 17 00:00:00 2001
From: Yanick Champoux <yanick@babyl.ca>
Date: Tue, 21 Dec 2021 15:03:45 -0500
Subject: [PATCH] 2021-21

---
 2021/21/part1.mjs | 30 ++++++++++++++++++++++++++++++
 2021/21/part2.mjs | 42 ++++++++++++++++++++++++++++++++++++++++++
 2021/21/sample    |  2 ++
 2021/21/test.mjs  | 20 ++++++++++++++++++++
 4 files changed, 94 insertions(+)
 create mode 100644 2021/21/part1.mjs
 create mode 100644 2021/21/part2.mjs
 create mode 100644 2021/21/sample
 create mode 100644 2021/21/test.mjs

diff --git a/2021/21/part1.mjs b/2021/21/part1.mjs
new file mode 100644
index 0000000..f6cdfc2
--- /dev/null
+++ b/2021/21/part1.mjs
@@ -0,0 +1,30 @@
+import fs from "fs-extra";
+import fp from "lodash/fp.js";
+import _ from "lodash";
+
+export const processInput = (input) => fs.readFile(input,'utf8').then(
+    content => content.split("\n").filter(x=>x).map(
+        line => parseInt(line.split(": ")[1])-1
+    )
+);
+
+export function solution(positions) {
+    let scores = [0,0];
+    let dice = 0;
+
+    MAIN: while( Math.max(...scores) < 1000 ) {
+        for( const player of [0,1] ) {
+            let add = 0;
+            _.range(3).forEach( () => {
+                dice++;
+                add+= dice;
+            } );
+            positions[player] = (positions[player] + add) % 10;
+            scores[player] += 1 + positions[player]
+            if(scores[player]>=1000) break MAIN;
+        }
+    }
+
+    return Math.min(...scores) * dice;
+
+}
diff --git a/2021/21/part2.mjs b/2021/21/part2.mjs
new file mode 100644
index 0000000..aa8f9fa
--- /dev/null
+++ b/2021/21/part2.mjs
@@ -0,0 +1,42 @@
+import fs from "fs-extra";
+import fp from "lodash/fp.js";
+import _ from "lodash";
+
+import * as p1 from "./part1.mjs";
+
+const cartesianProduct = (...rest) =>
+    rest.reduce(
+        (a, b) => a.flatMap((x) => b.map((y) => x.concat([y]))),
+        [[]]
+    );
+
+const dimensions = cartesianProduct(
+    _.range(1, 4),
+    _.range(1, 4),
+    _.range(1, 4)
+).map(fp.sum);
+
+function resolveGame(p1, p2, s1, s2, f) {
+    let wins = 0;
+    let loses = 0;
+
+    dimensions.forEach((points) => {
+        const newPosition = (p1 + points) % 10;
+        const newScore = newPosition + 1 + s1;
+        if (newScore >= 21) {
+            wins++;
+            return;
+        }
+        const next = f(p2, newPosition, s2, newScore, f);
+        wins += next[1];
+        loses += next[0];
+    });
+
+    return [wins, loses];
+}
+
+export function solution(positions) {
+    const res = _.memoize(resolveGame, (...args) => args.join("-"));
+
+    return Math.max(...res(...positions, 0, 0, res));
+}
diff --git a/2021/21/sample b/2021/21/sample
new file mode 100644
index 0000000..3f69194
--- /dev/null
+++ b/2021/21/sample
@@ -0,0 +1,2 @@
+Player 1 starting position: 4
+Player 2 starting position: 8
diff --git a/2021/21/test.mjs b/2021/21/test.mjs
new file mode 100644
index 0000000..4cf8e08
--- /dev/null
+++ b/2021/21/test.mjs
@@ -0,0 +1,20 @@
+// https://adventofcode.com/2021/day/21
+
+import tap from "tap";
+import fs from "fs-extra";
+
+import * as p1 from "./part1.mjs";
+import * as p2 from "./part2.mjs";
+
+const sample = p1.processInput('sample');
+const input = p1.processInput('input');
+
+tap.test("part1", async (t) => {
+    t.equal(p1.solution(await sample),739785 );
+    t.equal(p1.solution(await input), 916083);
+});
+
+tap.test("part2", async (t) => {
+    t.equal(p2.solution(await p1.processInput('sample')), 444356092776315);
+    t.equal(p2.solution(await p1.processInput('input')), 49982165861983);
+});