part 1

2021/09/part1.mjs

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+import fs from "fs-extra";
+import fp from "lodash/fp.js";
+import _ from "lodash";
+
+export const processInput = (filename) => fs.readFile(filename,'utf8').then(
+    content => content.split("\n").filter(x=>x).map(
+        lines => lines.split('').map(x => parseInt(x))
+    )
+);
+
+export const genNeighbours = (maxX,maxY) => (x,y) =>
+    [ [-1,0], [1,0], [0,1], [0,-1] ].map(
+        delta => _.zip(delta,[x,y]).map(_.sum)
+    ).filter( ([x,y]) => {
+        if(x<0 || y<0 ) return false;
+        if( x>= maxX || y>= maxY ) return false;
+        return true;
+    } );
+
+const genCoords = grid => ([x,y]) => grid[x][y];
+
+export function solution(grid) {
+    const seen = grid.map( () => [] );
+    let risk = 0;
+
+    const neighbours = genNeighbours(grid.length,grid[0].length);
+    const coords = genCoords(grid);
+
+    for( const x of _.range(grid.length) ) {
+        for( const y of _.range(grid[x].length) ) {
+            if( seen[x][y] ) continue;
+
+            let lowest = true;
+            for( const n of neighbours(x,y) ) {
+                if( coords(n) > grid[x][y] ) {
+                    seen[n[0]][n[1]] = true;
+                } else if ( coords(n) == grid[x][y] ) {
+                    seen[n[0]][n[1]] = true;
+                    lowest = false;
+                } else {
+                    lowest = false;
+                }
+            }
+
+            if(lowest) {
+                risk += 1 + grid[x][y];
+            }
+            seen[x][y] = true;
+
+        }
+    }
+
+    return risk;
+}

2021/09/part2.mjs

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+import fs from "fs-extra";
+import fp from "lodash/fp.js";
+import _ from "lodash";
+
+import * as p1 from './part1.mjs';
+
+export function solution(input) {
+}

2021/09/sample

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+2199943210
+3987894921
+9856789892
+8767896789
+9899965678

2021/09/test.mjs

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+// https://adventofcode.com/2021/day/09
+
+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.match(p1.genNeighbours(10,10)(0,0), [
+        [1,0],[0,1]
+]);
+    t.equal(p1.solution(await sample), 15);
+    t.equal(p1.solution(await input), 550);
+});
+
+tap.test("part2", async (t) => {
+    /* t.equal(p2.solution(await sample, 256), 26984457539); */
+    /* t.equal(p2.solution(await input, 256), 1622533344325); */
+});