From 983000000fdd92cee5029c2c2f94a607c9c31389 Mon Sep 17 00:00:00 2001
From: Jan Tuomi <jans.tuomi@gmail.com>
Date: Thu, 3 Dec 2020 10:29:14 +0200
Subject: Solve 3.2

---
 day3/index.ts | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/day3/index.ts b/day3/index.ts
index 6dd8168..3f40f60 100644
--- a/day3/index.ts
+++ b/day3/index.ts
@@ -1,9 +1,22 @@
 import { Observable, of } from "rxjs";
-import { concatAll, count, filter, map, take, tap } from 'rxjs/operators';
+import { concatAll, count, filter, groupBy, map, mergeMap, reduce, take, tap } from 'rxjs/operators';
 import { ExerciseModuleFunc } from "../types";
 
 type Coords = [number, number];
 
+const SLOPES: Coords[] = [
+  [1, 1],
+  [3, 1],
+  [5, 1],
+  [7, 1],
+  [1, 2]
+];
+
+interface Observation {
+  slope: Coords;
+  coords: Coords;
+}
+
 const day3: ExerciseModuleFunc = async (input: string) => {
   const lines = input.split("\n");
   const my = lines.length;
@@ -11,18 +24,23 @@ const day3: ExerciseModuleFunc = async (input: string) => {
 
   const isTree = (x: number, y: number): boolean => lines[y][x % mx] === "#";
 
-  const indexObs = new Observable<Coords>(sub => {
-    for (let y = 0, x = 0; y < my; y += 1, x += 3) {
-      if (isTree(x, y)) {
-        sub.next([x, y]);
+  const indexObs = new Observable<Observation>(sub => {
+    for (const slope of SLOPES) {
+      for (let y = 0, x = 0; y < my; y += slope[1], x += slope[0]) {
+        if (isTree(x, y)) {
+          sub.next({ slope, coords: [x, y] });
+        }
       }
     }
+
     sub.complete();
   })
 
   const prom1 = indexObs.pipe(
+    groupBy(obs => obs.slope),
+    mergeMap((grp$) => grp$.pipe(count())),
     tap(console.log),
-    count()
+    reduce((acc, val) => acc * val)
   ).toPromise();
 
   return Promise.all([prom1]);
-- 
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