solve spiral matrix problem

spiral_matrix.py

@@ -0,0 +1,120 @@
+class Solution:
+  def spiral_order_recursive(self, matrix):
+    """
+      Given a matrix of m x n elements (m rows, n columns),
+      return all elements of the matrix in spiral order
+      https://leetcode.com/problems/spiral-matrix/
+    """
+    def do_spiral(matrix, acc):
+      # base case of empty arr
+      if matrix == []: return acc
+
+      # # base case of [[1,2]]
+      if len(matrix) == 1:
+        for elem in matrix[0]:
+          acc.append(elem)
+
+        return acc
+      max_idx = len(matrix) - 1
+
+      # let's spiral across, down, and reverse across
+      for idx, elem in enumerate(matrix):
+        if idx == 0:
+          for e in elem:
+            acc.append(e)
+        elif idx == max_idx:
+          for e in reversed(elem):
+            acc.append(e)
+        else:
+          acc.append(elem[-1])
+
+      # if there is only one column it's already been used
+      # bye we are done no spiraling up needed
+      if len(matrix[0]) == 1: return acc
+
+      # let's spiral up
+      for idx, elem in enumerate(reversed(matrix)):
+        if idx != 0 and idx != max_idx:
+          acc.append(elem[0])
+
+      # let's recurse
+      # if only 2 columns, they've all been used. return acc
+      if len(matrix[0]) == 2: return acc
+      # if there is only one column it's already been used bye
+
+      # let's make the matrix smaller for recursion
+      # get rid of the first and last rows
+      # they've already been used
+      # note: slicing is expensive.
+      # cos we are copying everything except for the outer ring.
+      # optimization:
+      # instead of slicing the matrix, keep track of indexes for
+      # what regions of the matrix you're working with
+      # keep track of top left (1,1) and bottom right (4,4)
+      # top left increases by (1,1) bottom right decreases by (1,1)
+
+      mtrx = matrix[1:-1]
+      # get rid of the first and last items in the remaining lists
+      # they've already been used
+      for idx, elem in enumerate(mtrx):
+        mtrx[idx] = elem[1:-1]
+
+      return do_spiral(mtrx, acc)
+
+    return do_spiral(matrix, [])
+
+  def spiral_order_iterative(self):
+    """
+    solve this the iterative way
+
+    plan:
+    - keep track of where you're moving
+    - if you're moving to the right, i, j i = row, j = column
+    - changes by (0,1) (row stays same, column increases by 1) velocity is (0,1)
+    - figure out velocity for all directions (0,1), (1,0), (0,-1), (-1,0)
+    - keep moving. see whether it's a valid move. if it is, you move, if it's not, you turn
+    - for loop that moves (n*m)-1 times cos you don't move on first step.
+    - eg: matrix is 3 rows and 4 columns, 3x4 = 12. you move 11 times
+    - keep track of coordinates you've already processed. eg: change item to nil. so if nil, turn
+    """
+    pass
+
+class Test:
+  def test(self):
+    s = Solution()
+    self.test_spiral_order(s)
+
+  def test_spiral_order(self, s):
+    matrices = [
+      [],
+      [[1,2]],
+      [[1,2], [3,4]],
+      [[1,2], [3,4], [5,6]],
+      [[1, 2, 3, 4], [5, 6, 7, 8], [9,10,11,12]],
+      [[7], [9], [6]],
+      [[1,11], [2,12], [3,13], [4,14], [5,15], [6,16], [7,17], [8,18], [9,19], [10,20]],
+      [[1,2,3,4], [5,6,7,8], [9,10,11,12], [13,14,15,16]]
+    ]
+
+    expected_results = [
+      [],
+      [1,2],
+      [1,2,4,3],
+      [1,2,4,6,5,3],
+      [1,2,3,4,8,12,11,10,9,5,6,7],
+      [7,9,6],
+      [1,11,12,13,14,15,16,17,18,19,20,10,9,8,7,6,5,4,3,2],
+      [1,2,3,4,8,12,16,15,14,13,9,5,6,7,11,10]
+    ]
+
+    for idx, m in enumerate(matrices):
+      try:
+        result = s.spiral_order_recursive(m)
+        assert result == expected_results[idx]
+      except AssertionError:
+        print(m)
+        print(result)
+        print(expected_results[idx])
+
+t = Test()
+t.test()