CTCI 3.1

Python

Author: kyle8998

CTCI/Chapter3/3.1-Three_In_One.py

@@ -0,0 +1,53 @@
+# CTCI 3.1
+# Three in One
+
+import unittest
+
+class ThreeStacks():
+    def __init__(self):
+        self.array = [None, None, None]
+        self.current = [0, 1, 2]
+        
+    def push(self, item, stack_number):
+        if not stack_number in [0, 1, 2]:
+            raise Exception("Bad stack number")
+        while len(self.array) <= self.current[stack_number]:
+            self.array += [None] * len(self.array)
+        self.array[self.current[stack_number]] = item
+        self.current[stack_number] += 3
+    
+    def pop(self, stack_number):
+        if not stack_number in [0, 1, 2]:
+            raise Exception("Bad stack number")
+        if self.current[stack_number] > 3:
+            self.current[stack_number] -= 3
+        item = self.array[self.current[stack_number]]
+        self.array[self.current[stack_number]] = None
+        return item
+    
+
+#-------------------------------------------------------------------------------
+# CTCI Solution 
+
+#-------------------------------------------------------------------------------
+#Testing
+
+class Test(unittest.TestCase):
+  def test_three_stacks(self):
+    three_stacks = ThreeStacks()
+    three_stacks.push(101, 0)
+    three_stacks.push(102, 0)
+    three_stacks.push(103, 0)
+    three_stacks.push(201, 1)
+    self.assertEqual(three_stacks.pop(0), 103)
+    self.assertEqual(three_stacks.pop(1), 201)
+    self.assertEqual(three_stacks.pop(1), None)
+    self.assertEqual(three_stacks.pop(2), None)
+    three_stacks.push(301, 2)
+    three_stacks.push(302, 2)
+    self.assertEqual(three_stacks.pop(2), 302)
+    self.assertEqual(three_stacks.pop(2), 301)
+    self.assertEqual(three_stacks.pop(2), None)
+
+if __name__ == "__main__":
+  unittest.main()

README.md

@@ -118,6 +118,8 @@ Cracking the Coding Interview 6th Edition Python Solutions
 | 2.6|            | Palindrome                                                                                   | [Python](CTCI/Chapter2/2.6-Palindrome.py)                       |
 | 2.7|            | Intersection                                                                                 | [Python](CTCI/Chapter2/2.7-Intersection.py)                     |
 | 2.8|            | Loop Detection                                                                               | [Python](CTCI/Chapter2/2.8-Loop_Detection.py)                   |
+|    |            |                                                                                              |                                                                 |
+| 3.1|            | Three in One                                                                                 | [Python](CTCI/Chapter2/3.1-Three_In_One.py)                     |
 
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