day 4

2025-12-04 11:06:20 +01:00
parent b86faabc79
commit d1e6ac0b74
4 changed files with 331 additions and 0 deletions
@@ -0,0 +1,86 @@
+import fs from 'node:fs';
+
+
+const file = fs.readFileSync('./2025/inputs/4').toString();
+const lines = file.split("\n").map(e => e.split(""))
+const yLength = lines.length
+const xLength = lines[0].length
+
+const table: Node[][] = []
+const nodes: Node[] = []
+
+class Node {
+    neighbours = 0
+    constructor(public x: number, public y: number, public isPaper: boolean) {
+        nodes.push(this)
+    }
+
+    /**
+     * Because we iterate from N-W to S-E
+     * We only need to lookup the S-E neighbours 
+     * x x x
+     * x o c
+     * c c c
+     */
+
+    public calculateNeighbours() {
+        // x x x
+        // x o c
+        // x x x
+        if (this.x + 1 < xLength) {
+            const w = table[this.y][this.x + 1]
+            if (w.isPaper) {
+                this.neighbours++
+            }
+            if (this.isPaper) {
+                w.neighbours++
+            }
+        }
+
+        if (this.y + 1 < yLength) {
+            // x x x
+            // x o x
+            // x c x
+            const s = table[this.y + 1][this.x]
+            if (s.isPaper) {
+                this.neighbours++
+
+            }
+            if (this.isPaper) {
+                s.neighbours++
+            }
+            // x x x
+            // x o x
+            // x x c
+            if (this.x + 1 < xLength) {
+                const se = table[this.y + 1][this.x + 1]
+                if (se.isPaper) {
+                    this.neighbours++
+                }
+                if (this.isPaper) {
+                    se.neighbours++
+                }
+
+            }
+
+            // x x x
+            // x o x
+            // c x x
+            if (this.x - 1 >= 0) {
+                const sw = table[this.y + 1][this.x - 1]
+                if (sw.isPaper) {
+                    this.neighbours++
+                }
+                if (this.isPaper) {
+                    sw.neighbours++
+                }
+
+            }
+        }
+    }
+}
+
+table.push(...lines.map((l, i) => l.map((e, j) => new Node(j, i, e == "@"))))
+nodes.forEach(n => n.calculateNeighbours())
+console.log(nodes.filter(n => n.neighbours < 4 && n.isPaper).length)
+