add solution: spiral-matrix

Author: dusunax

spiral-matrix/dusunax.py

@@ -0,0 +1,52 @@
+'''
+# 54. Spiral Matrix
+
+to traverse the matrix in a spiral order:
+1. do boundary-tracking
+2. iterate in layers
+  - move right, move down, move left, move up
+  - shrink the boundaries
+4. return the result
+
+# Time and Space Complexity
+
+```
+TC: O(m * n)
+SC: O(1)
+```
+
+#### TC is O(m * n):
+move through the 2D matrix just once. = O(m * n)
+
+#### SC is O(1):
+result list is excluded from auxiliary space, so it's = O(1)
+'''
+
+class Solution:
+    def spiralOrder(self, matrix: List[List[int]]) -> List[int]:
+        top = 0
+        left = 0
+        bottom = len(matrix) - 1
+        right = len(matrix[0]) - 1
+        result = [] # SC: O(1)
+
+        while top <= bottom and left <= right:
+            for i in range(left, right + 1):
+                result.append(matrix[top][i])
+            top += 1
+
+            for i in range(top, bottom + 1):
+                result.append(matrix[i][right])
+            right -= 1
+
+            if top <= bottom:
+                for i in range(right, left - 1, -1):
+                    result.append(matrix[bottom][i])
+                bottom -= 1
+            
+            if left <= right:
+                for i in range(bottom, top - 1, -1):
+                    result.append(matrix[i][left])
+                left += 1
+        
+        return result