2024D09: Part 2

martapanc · Dec 10, 2024 · 884eef3 · 884eef3
1 parent 276c46d
commit 884eef3
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Showing 2 changed files with 82 additions and 7 deletions.
diff --git a/2024/src/2024/day09/day09.test.ts b/2024/src/2024/day09/day09.test.ts
@@ -7,9 +7,14 @@ describe('2024 Day 9', () => {
         expect(await part1('input')).toEqual(6435922584968);
     });
 
+    // 00...111...2...333.44.5555.6666.777.888899
+    // 0099.111...2...333.44.5555.6666.777.8888..
+    // 0099.1117772...333.44.5555.6666.....8888..
+    // 0099.111777244.333....5555.6666.....8888..
+    // 00992111777.44.333....5555.6666.....8888..
     test('Part 2', async () => {
-        // expect(await part2('testInput1')).toEqual(31);
-        // expect(await part2('input')).toEqual(29379307);
+        expect(await part2('testInput1')).toEqual(2858);
+        expect(await part2('input')).toEqual(6469636832766);
     });
 });
 

diff --git a/2024/src/2024/day09/day09.ts b/2024/src/2024/day09/day09.ts
@@ -6,7 +6,7 @@ export async function part1(inputFile: string) {
 }
 
 export async function part2(inputFile: string) {
-    return await day9(inputFile);
+    return await day9(inputFile, fragmentAndCalcChecksum2);
 }
 
 async function day9(inputFile: string, calcFn?: (line: string) => number) {
@@ -60,11 +60,77 @@ function fragmentAndCalcChecksum(line: string) {
         }
     }
 
-    return collapseAndCalcChecksum(expandedDisk);
+    return calcChecksum(expandedDisk);
 }
 
+function fragmentAndCalcChecksum2(line: string) {
+    const expandedDisk = expandDiskMap(line);
+
+    const highestBlockIndex = expandedDisk.length - 1;
+    const highestBlock = expandedDisk[highestBlockIndex];
+
+    let blockId: number = Number.parseInt(Object.keys(highestBlock)[0]);
+
+    while (blockId > 0) {
+        const blockIndex = expandedDisk.findIndex(block => Number(Object.keys(block)[0]) === blockId);
+        const block  = expandedDisk[blockIndex];
+        const blockLength = block?.[blockId]!;
+
+        const firstLargeEnoughEmptyIndex = expandedDisk.findIndex((item) => '.' in item && item['.'] as number >= blockLength );
+        if (firstLargeEnoughEmptyIndex === -1 || firstLargeEnoughEmptyIndex > blockIndex) {
+            blockId--;
+            continue;
+        }
+        let firstLargeEnoughEmptyBlock = expandedDisk[firstLargeEnoughEmptyIndex];
+        const [dot, emptyLength] = Object.entries(firstLargeEnoughEmptyBlock)[0];
+
+        let newCurrentBlockIndex = blockIndex;
+
+        if (blockLength < emptyLength || blockLength === emptyLength) {
+
+            if (blockLength < emptyLength) {
+                firstLargeEnoughEmptyBlock = { [blockId]: blockLength };
+                expandedDisk[firstLargeEnoughEmptyIndex] = firstLargeEnoughEmptyBlock;
+
+                const remainingEmptyBlock = {[dot]: emptyLength - blockLength };
+                expandedDisk.splice(firstLargeEnoughEmptyIndex + 1, 0, remainingEmptyBlock);
+
+                expandedDisk.splice(blockIndex + 1, 1, {'.': blockLength});
+
+                // Two blocks (one full, one empty) were created, so bumping block index
+                newCurrentBlockIndex++;
+            } else if (blockLength === emptyLength) {
+                firstLargeEnoughEmptyBlock = { [blockId]: blockLength };
+                expandedDisk[firstLargeEnoughEmptyIndex] = firstLargeEnoughEmptyBlock;
+
+                expandedDisk.splice(blockIndex, 1, {'.': emptyLength});
+            }
+
+            // Merge consecutive empty blocks if newly formed
+            const prevBlock = expandedDisk[newCurrentBlockIndex - 1];
+            const currentBlock = expandedDisk[newCurrentBlockIndex];
+            const nextBlock = expandedDisk[newCurrentBlockIndex + 1];
+
+            if (nextBlock && '.' in currentBlock && '.' in nextBlock) {
+                const nextBlockLength = nextBlock['.'];
+                expandedDisk.splice(newCurrentBlockIndex, 2, { '.': blockLength + nextBlockLength });
+            }
+            if ('.' in prevBlock && '.' in currentBlock) {
+                const prevBlockLength = prevBlock['.'];
+                expandedDisk.splice(newCurrentBlockIndex - 1, 2, { '.': prevBlockLength + expandedDisk[newCurrentBlockIndex]['.'] })
+            }
+        }
+
+        blockId--;
+    }
+
+    return calcChecksum(expandedDisk);
+}
+
+type Block = { [key: number | string]: number };
+
 export function expandDiskMap(line: string) {
-    const list: object[] = [];
+    const list: Block[] = [];
 
     let blockIdx = 0;
     line.split('').forEach((item, index) => {
@@ -82,14 +148,18 @@ export function expandDiskMap(line: string) {
     return list;
 }
 
-export function collapseAndCalcChecksum(list: object[]) {
+export function calcChecksum(list: object[]) {
     let checksum = 0;
     let currentPosition = 0;
 
     for (const block of list) {
         const [blockId, length] = Object.entries(block)[0];
-        const id = parseInt(blockId, 10);
         const len = length;
+        if (blockId === '.') {
+            currentPosition += len;
+            continue;
+        }
+        const id = parseInt(blockId, 10);
 
         for (let i = 0; i < len; i++) {
             checksum += id * (currentPosition + i);