Add spiral matrix (#354)

config.json

@@ -646,6 +646,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 3
+      },
+      {
+        "slug": "spiral-matrix",
+        "name": "Spiral Matrix",
+        "uuid": "7d5230f7-6aa2-4d57-9618-83c509630360",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
       }
     ]
   },

exercises/practice/spiral-matrix/.docs/instructions.md

@@ -0,0 +1,24 @@
+# Instructions
+
+Given the size, return a square matrix of numbers in spiral order.
+
+The matrix should be filled with natural numbers, starting from 1 in the top-left corner, increasing in an inward, clockwise spiral order, like these examples:
+
+## Examples
+
+### Spiral matrix of size 3
+
+```text
+1 2 3
+8 9 4
+7 6 5
+```
+
+### Spiral matrix of size 4
+
+```text
+ 1  2  3 4
+12 13 14 5
+11 16 15 6
+10  9  8 7
+```

exercises/practice/spiral-matrix/.meta/config.json

@@ -0,0 +1,17 @@
+{
+  "authors": ["blakelewis"],
+  "files": {
+    "solution": [
+      "spiral-matrix.rkt"
+    ],
+    "test": [
+      "spiral-matrix-test.rkt"
+    ],
+    "example": [
+      ".meta/example.rkt"
+    ]
+  },
+  "blurb": "Given the size, return a square matrix of numbers in spiral order.",
+  "source": "Reddit r/dailyprogrammer challenge #320 [Easy] Spiral Ascension.",
+  "source_url": "https://web.archive.org/web/20230607064729/https://old.reddit.com/r/dailyprogrammer/comments/6i60lr/20170619_challenge_320_easy_spiral_ascension/"
+}

exercises/practice/spiral-matrix/.meta/example.rkt

@@ -0,0 +1,28 @@
+#lang racket
+
+(provide spiral-matrix)
+
+(define (extract-row r coord)
+  (let* ([row (filter (λ (c) (= (caar c) r)) coord)]
+         [sorted-row (sort row < #:key cdar)])
+    (map cdr sorted-row)))
+
+(define (take-step x y dx dy n h)
+  (let ([x1 (+ x dx)] [y1 (+ y dy)])
+    (if (or (negative? x1) (negative? y1)
+            (= x1 n) (= y1 n) (hash-has-key? h (cons y1 x1)))
+      (values (- x dy) (+ y dx) (- dy) dx)
+      (values x1 y1 dx dy))))
+
+(define (coordinates n)
+  (let ([h (make-hash)])
+    (for/fold
+      ([x 0] [y 0] [dx 1] [dy 0] #:result (hash->list h))
+      ([i (in-inclusive-range 1 (* n n))])
+      (hash-set! h (cons y x) i)
+      (take-step x y dx dy n h))))
+
+(define (spiral-matrix n)
+  (let ([coord (coordinates n)])
+    (for/list ([i (in-range n)])
+      (extract-row i coord))))

exercises/practice/spiral-matrix/.meta/tests.toml

@@ -0,0 +1,28 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[8f584201-b446-4bc9-b132-811c8edd9040]
+description = "empty spiral"
+
+[e40ae5f3-e2c9-4639-8116-8a119d632ab2]
+description = "trivial spiral"
+
+[cf05e42d-eb78-4098-a36e-cdaf0991bc48]
+description = "spiral of size 2"
+
+[1c475667-c896-4c23-82e2-e033929de939]
+description = "spiral of size 3"
+
+[05ccbc48-d891-44f5-9137-f4ce462a759d]
+description = "spiral of size 4"
+
+[f4d2165b-1738-4e0c-bed0-c459045ae50d]
+description = "spiral of size 5"

exercises/practice/spiral-matrix/spiral-matrix-test.rkt

@@ -0,0 +1,46 @@
+#lang racket/base
+
+(require "spiral-matrix.rkt")
+
+(module+ test
+  (require rackunit rackunit/text-ui))
+
+(module+ test
+  (define suite
+    (test-suite "spiral matrix tests"
+      (test-equal? "empty spiral"
+        (spiral-matrix 0)
+        '())
+
+      (test-equal? "trivial spiral"
+        (spiral-matrix 1)
+        '((1)))
+
+      (test-equal? "spiral of size 2"
+        (spiral-matrix 2)
+        '((1 2)
+          (4 3)))
+
+      (test-equal? "spiral of size 3"
+        (spiral-matrix 3)
+        '((1 2 3)
+          (8 9 4)
+          (7 6 5)))
+
+      (test-equal? "spiral of size 4"
+        (spiral-matrix 4)
+        '((1 2 3 4)
+          (12 13 14 5)
+          (11 16 15 6)
+          (10 9 8 7)))
+
+      (test-equal? "spiral of size 5"
+        (spiral-matrix 5)
+        '((1 2 3 4 5)
+          (16 17 18 19 6)
+          (15 24 25 20 7)
+          (14 23 22 21 8)
+          (13 12 11 10 9)))))
+
+  (run-tests suite))
+

exercises/practice/spiral-matrix/spiral-matrix.rkt

@@ -0,0 +1,6 @@
+#lang racket
+
+(provide spiral-matrix)
+
+(define (spiral-matrix n)
+  (error "Not implemented yet"))