Working part one and two

Changed the export storage format, namely, the safe squares are
represented by a `1` instead of a `0`. Makes the reduce a _bit_ easier.

2016/18/grid.js

@@ -1,5 +1,54 @@
 class Grid {
-
+    constructor(first_row) {
+        this.grid = [first_row.slice(0)];
+    }
+
+    /**
+     * @param {int} n - Number of rows to add onto grid
+     */
+    addRows(n) {
+        for (let i = 0; i < n; i++) {
+            let row = [];
+            let row_above = this.grid[this.grid.length - 1];
+            row_above.forEach((tile, t) => {
+                let left = row_above[t - 1];
+                let center = tile;
+                let right = row_above[t + 1];
+
+                // `1` is a safe tile
+                if (left === undefined) left = 1;
+                if (right === undefined) right = 1;
+
+                /**
+                 * A new tile is a _trap_ only in one of the following situations:
+                 *
+                 * - Its _left_ and _center_ tiles are traps, but its _right_ tile is not.
+                 * - Its _center_ and _right_ tiles are traps, but its _left_ tile is not.
+                 * - Only its _left_ tile is a trap.
+                 * - Only its _right_ tile is a trap.
+                 */
+                if (
+                    (left === 0 && center === 0 && right === 1) ||
+                    (left === 1 && center === 0 && right === 0) ||
+                    (left === 0 && center === 1 && right === 1) ||
+                    (left === 1 && center === 1 && right === 0)
+                ) {
+                    // Trap tile
+                    row.push(0);
+                } else {
+                    // Safe tile
+                    row.push(1);
+                }
+            });
+
+            this.grid.push(row);
+        }
+    }
+
+    // Assumes safe tiles are stored as a `1`
+    countSafeTiles() {
+        return this.grid.map(row => row.reduce((a, b) => a + b, 0)).reduce((a, b) => a + b, 0);
+    }
 }
 
 module.exports = Grid;

2016/18/input.js

@@ -1,13 +1,15 @@
-// `0` is safe, `1` is trap
+// `1` is safe, `0` is trap
+// This is because I'm counting safe tiles for the puzzle,
+// so its easier to reduce them if they are equal to `1`.
 module.exports = {
     sampleInput: {
         // ..^^.
         // .^^^^
         // ^^..^
         small: [
-            [0, 0, 1, 1, 0],
-            [0, 1, 1, 1, 1],
             [1, 1, 0, 0, 1],
+            [1, 0, 0, 0, 0],
+            [0, 0, 1, 1, 0],
         ],
 
         // .^^.^.^^^^
@@ -21,17 +23,17 @@ module.exports = {
         // .^^^..^.^^
         // ^^.^^^..^^
         larger: [
-            [0, 1, 1, 0, 1, 0, 1, 1, 1, 1],
-            [1, 1, 1, 0, 0, 0, 1, 0, 0, 1],
-            [1, 0, 1, 1, 0, 1, 0, 1, 1, 0],
-            [0, 0, 1, 1, 0, 0, 0, 1, 1, 1],
-            [0, 1, 1, 1, 1, 0, 1, 1, 0, 1],
-            [1, 1, 0, 0, 1, 0, 1, 1, 0, 0],
-            [1, 1, 1, 1, 0, 0, 1, 1, 1, 0],
-            [1, 0, 0, 1, 1, 1, 1, 0, 1, 1],
-            [0, 1, 1, 1, 0, 0, 1, 0, 1, 1],
-            [1, 1, 0, 1, 1, 1, 0, 0, 1, 1],
+            [1, 0, 0, 1, 0, 1, 0, 0, 0, 0],
+            [0, 0, 0, 1, 1, 1, 0, 1, 1, 0],
+            [0, 1, 0, 0, 1, 0, 1, 0, 0, 1],
+            [1, 1, 0, 0, 1, 1, 1, 0, 0, 0],
+            [1, 0, 0, 0, 0, 1, 0, 0, 1, 0],
+            [0, 0, 1, 1, 0, 1, 0, 0, 1, 1],
+            [0, 0, 0, 0, 1, 1, 0, 0, 0, 1],
+            [0, 1, 1, 0, 0, 0, 0, 1, 0, 0],
+            [1, 0, 0, 0, 1, 1, 0, 1, 0, 0],
+            [0, 0, 1, 0, 0, 0, 1, 1, 0, 0],
         ],
     },
-    input: [0, 1, 1, 0, 1, 1, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 1, 1, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 1, 0, 1, 1, 1, 0, 0, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 0, 0, 1, 1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 0, 1, 0],
+    input: [1, 0, 0, 1, 0, 0, 0, 1, 1, 0, 1, 0, 1, 1, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 1, 1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 1, 0, 1],
 };

2016/18/part-one.js

@@ -1,3 +1,7 @@
 const assert = require('assert');
 const Grid = require('./grid');
 const { input, sampleInput } = require('./input');
+
+let grid = new Grid(input);
+grid.addRows(39);
+console.log(grid.countSafeTiles());

2016/18/part-two.js

@@ -1,3 +1,7 @@
 const assert = require('assert');
 const Grid = require('./grid');
 const { input, sampleInput } = require('./input');
+
+let grid = new Grid(input);
+grid.addRows(400000 - 1);
+console.log(grid.countSafeTiles());