spiral-matrix: implement.

config.json

@@ -724,6 +724,18 @@
         "text formatting"
       ]
     },
+    {
+      "uuid": "666fda78-851e-4bb0-a416-953528f46bd7",
+      "slug": "spiral-matrix",
+      "core": false,
+      "unlocked_by": null,
+      "difficulty": 2,
+      "topics": [
+        "algorithms",
+        "control-flow (loops)",
+        "lists"
+      ]
+    },
     {
       "uuid": "ecc97fc6-2e72-4325-9b67-b56c83b13a91",
       "slug": "grep",

exercises/spiral-matrix/README.md

@@ -0,0 +1,32 @@
+# Spiral Matrix
+
+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:
+
+###### Spiral matrix of size 3
+
+```plain
+1 2 3
+8 9 4
+7 6 5
+```
+
+###### Spiral matrix of size 4
+
+```plain
+ 1  2  3 4
+12 13 14 5
+11 16 15 6
+10  9  8 7
+```
+## Source
+
+Reddit r/dailyprogrammer challenge #320 [Easy] Spiral Ascension.
+[https://www.reddit.com/r/dailyprogrammer/comments/6i60lr/20170619_challenge_320_easy_spiral_ascension/](https://www.reddit.com/r/dailyprogrammer/comments/6i60lr/20170619_challenge_320_easy_spiral_ascension/)
+
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

exercises/spiral-matrix/example.py

@@ -0,0 +1,11 @@
+def spiral(size):
+    m = [[0] * size for i in range(size)]
+    dx, dy = [0, 1, 0, -1], [1, 0, -1, 0]
+    x, y, c = 0, -1, 1
+    for k in range(2*size - 1):
+        for j in range((2*size - k) // 2):
+            x += dx[k % 4]
+            y += dy[k % 4]
+            m[x][y] = c
+            c += 1
+    return m

exercises/spiral-matrix/spiral_matrix.py

@@ -0,0 +1,2 @@
+def spiral(size):
+    pass

exercises/spiral-matrix/spiral_matrix_test.py

@@ -0,0 +1,40 @@
+import unittest
+
+from spiral_matrix import spiral
+
+# Tests are based on the version 1.0.0 of:
+# https://github.com/exercism/problem-specifications/blob/master/exercises/spiral-matrix/canonical-data.json
+
+
+class SpiralMatrixTest(unittest.TestCase):
+    def test_spiral_matrix_of_0(self):
+        self.assertEqual(spiral(0), [])
+
+    def test_spiral_matrix_of_1(self):
+        self.assertEqual(spiral(1), [[1]])
+
+    def test_spiral_matrix_of_2(self):
+        self.assertEqual(spiral(2), [[1, 2],
+                                     [4, 3]])
+
+    def test_spiral_matrix_of_3(self):
+        self.assertEqual(spiral(3), [[1, 2, 3],
+                                     [8, 9, 4],
+                                     [7, 6, 5]])
+
+    def test_spiral_matrix_of_4(self):
+        self.assertEqual(spiral(4), [[1,  2,  3,  4],
+                                     [12, 13, 14, 5],
+                                     [11, 16, 15, 6],
+                                     [10, 9,  8,  7]])
+
+    def test_spiral_matrix_of_5(self):
+        self.assertEqual(spiral(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]])
+
+
+if __name__ == '__main__':
+    unittest.main()