1 files changed, 27 insertions, 2 deletions
diff --git a/day-5/script.ts b/day-5/script.ts
index 2d18477..f0eb76e 100644
--- a/day-5/script.ts
+++ b/day-5/script.ts
@@ -3,8 +3,20 @@ import fs from "fs";
 const input = fs.readFileSync("./input.txt").toString();
 
 const [seedStr, ...mapStrings] = input.split("\n\n");
-
-const seeds = seedStr.match(/\d+/g)?.map(Number) || [];
+export function chunks<T>(data: Array<T>, chunkSize: number) {
+  return data.reduce((acc, value, index) => {
+    // Initialize a new chunk
+    if (index % chunkSize === 0) acc.push([]);
+    acc[acc.length - 1].push(value);
+    return acc;
+  }, [] as T[][]);
+}
+
+const seedRanges = chunks(seedStr.match(/\d+/g)?.map(Number) || [], 2).map(
+  ([start, size]) => {
+    return { start, size };
+  },
+);
 
 const maps = mapStrings.map((mapString) =>
   mapString
@@ -19,6 +31,19 @@ const maps = mapStrings.map((mapString) =>
     })),
 );
 
+// We dont need to inspect whole seed ranges, instead we only select "interesting points"
+// Interesting points lie at starts/end of ranges defined in our maps
+const seeds = maps
+  .flatMap((ranges) =>
+    ranges.flatMap((r) => [r.sourceStart, r.destinationStart + 1]),
+  )
+  .filter((breakpoint) =>
+    seedRanges.find(
+      (range) =>
+        breakpoint >= range.start && breakpoint < range.start + range.size,
+    ),
+  );
+
 const locationNumbers = seeds.map((seed) =>
   maps.reduce((currentNumber, mapRules) => {
     const validRule = mapRules.find(