2021-09

2021/09/part1.mjs

@@ -17,7 +17,7 @@ export const genNeighbours = (maxX,maxY) => (x,y) =>
         return true;
     } );
 
-const genCoords = grid => ([x,y]) => grid[x][y];
+export const genCoords = grid => ([x,y]) => grid[x][y];
 
 export function solution(grid) {
     const seen = grid.map( () => [] );

2021/09/part2.mjs

@@ -4,5 +4,41 @@ import _ from "lodash";
 
 import * as p1 from './part1.mjs';
 
-export function solution(input) {
+function getBasinSize( [x,y], grid, seen ) {
+    if( seen[x][y] ) return 0;
+
+    seen[x][y] = true;
+
+    if( grid[x][y] == 9 ) return 0;
+    let size = 1;
+
+    const neighbours = p1.genNeighbours(grid.length,grid[0].length);
+    const coords = p1.genCoords(grid);
+
+    neighbours(x,y).map( n => getBasinSize(n,grid,seen) ).forEach(
+        x => size+=x
+    );
+
+    return size;
+}
+
+export function solution(grid) {
+    const seen = grid.map( () => [] );
+    let basinSizes = [];
+
+
+    for( const x of _.range(grid.length) ) {
+        for( const y of _.range(grid[x].length) ) {
+            if( seen[x][y] ) continue;
+
+            if( grid[x][y] == 9 ) {
+                seen[x][y] = true;
+                continue;
+            }
+            basinSizes.push( getBasinSize([x,y],grid,seen));
+        }
+    }
+
+    basinSizes.sort( (a,b) => a < b ? 1 : -1 );
+    return basinSizes.splice(0,3).reduce( (a,b) => a*b ) ;
 }

2021/09/test.mjs

@@ -18,6 +18,6 @@ tap.test("part1", async (t) => {
 });
 
 tap.test("part2", async (t) => {
-    /* t.equal(p2.solution(await sample, 256), 26984457539); */
-    /* t.equal(p2.solution(await input, 256), 1622533344325); */
+    t.equal(p2.solution(await sample), 1134);
+    t.equal(p2.solution(await input), 1100682);
 });