day 4 complete

1 files changed, 99 insertions, 9 deletions

diff --git a/2022/day-04/day-04.ipynb b/2022/day-04/day-04.ipynb
index ef18f45..44c8980 100644
--- a/2022/day-04/day-04.ipynb
+++ b/2022/day-04/day-04.ipynb
@@ -5,30 +5,120 @@
    "metadata": {},
    "source": [
     "### Advent of Code 2022\n",
-    "#### Day 4:\n",
+    "#### Day 4: Camp Cleanup\n",
     "\n",
-    "**Part 1.**\n",
+    "Each elf in a pair of elves is assigned a range of ID numbers.\n",
     "\n",
-    "**Part 2.**"
+    "**Part 1.** How many pairs have one elf assigned to a range completely contained by the other's?\n",
+    "\n",
+    "**Part 2.** How many pairs have overlapping assignments?\n",
+    "\n",
+    "Since this problem heavily uses ranges, I'm using `rebellion/base/range` to do the heavy lifting."
    ]
   },
   {
    "cell_type": "code",
    "execution_count": 1,
-   "metadata": {},
+   "metadata": {
+    "vscode": {
+     "languageId": "racket"
+    }
+   },
    "outputs": [],
    "source": [
     "#lang iracket/lang #:require rackjure\n",
-    "(require advent-of-code)"
+    "(require advent-of-code\n",
+    "         relation\n",
+    "         rebellion/base/range)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "##### Part 1\n",
+    "\n",
+    "All the assignments look like `\"11-22,33-44\"`, so we write a function to extract the numbers from the string with a regex, decompose the values with structural matching, and construct a pair of [`rebellion` ranges](https://docs.racket-lang.org/rebellion/Ranges.html).\n",
+    "\n",
+    "Once we have the two ranges, we can use a predicate that tests if one completely contains the other or vice versa to count the corresponding assignments."
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 2,
+   "metadata": {
+    "vscode": {
+     "languageId": "racket"
+    }
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<code>550</code>"
+      ],
+      "text/plain": [
+       "550"
+      ]
+     },
+     "execution_count": 2,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "(define assignments (~> (fetch-aoc-input (find-session) 2022 4) string-split))\n",
+    "\n",
+    "(define (parse-range str)\n",
+    "  (match str\n",
+    "    [(regexp #px\"(\\\\d+)-(\\\\d+),(\\\\d+)-(\\\\d+)\" (list _ a b c d))\n",
+    "     (values (closed-range (->number a) (->number b)) (closed-range (->number c) (->number d)))]))\n",
+    "\n",
+    "(define (one-encloses-the-other? str)\n",
+    "  (define-values (range1 range2) (parse-range str))\n",
+    "  (or (range-encloses? range1 range2) (range-encloses? range2 range1)))\n",
+    "\n",
+    "(count one-encloses-the-other? assignments)\n"
+   ]
+  },
+  {
+   "cell_type": "markdown",
    "metadata": {},
-   "outputs": [],
    "source": [
-    "(fetch-aoc-input (find-session) 2022 4)"
+    "##### Part 2\n",
+    "\n",
+    "The procedure for part 2 is the same, just using the predicate for overlapping ranges instead."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {
+    "vscode": {
+     "languageId": "racket"
+    }
+   },
+   "outputs": [
+    {
+     "data": {
+      "text/html": [
+       "<code>931</code>"
+      ],
+      "text/plain": [
+       "931"
+      ]
+     },
+     "execution_count": 3,
+     "metadata": {},
+     "output_type": "execute_result"
+    }
+   ],
+   "source": [
+    "(define (one-overlaps-the-other? str)\n",
+    "  (define-values (range1 range2) (parse-range str))\n",
+    "  (range-overlaps? range1 range2))\n",
+    "\n",
+    "(count one-overlaps-the-other? assignments)\n"
    ]
   }
  ],
@@ -42,7 +132,7 @@
    "codemirror_mode": "scheme",
    "file_extension": ".rkt",
    "mimetype": "text/x-racket",
-   "name": "racket",
+   "name": "Racket",
    "pygments_lexer": "racket",
    "version": "8.7"
   },