Scissors - Maria M.

heaps/heap_sort.py

@@ -1,8 +1,16 @@
-
+from heaps.min_heap import MinHeap
 
 def heap_sort(list):
     """ This method uses a heap to sort an array.
-        Time Complexity:  ?
-        Space Complexity: ?
+        Time Complexity:  O(n log n)
+        Space Complexity: O(n)
     """
-    pass
+    heap = MinHeap()
+    sorted_list = []
+
+    for value in list:
+        heap.add(value)
+
+    while heap.store:
+        sorted_list.append(heap.remove())
+    return sorted_list

heaps/min_heap.py

@@ -1,5 +1,5 @@
 class HeapNode:
-  
+
     def __init__(self, key, value):
         self.key = key
         self.value = value
@@ -10,31 +10,57 @@ def __str__(self):
     def __repr__(self):
         return str(self.value)
 
-
-
 class MinHeap:
 
     def __init__(self):
         self.store = []
 
+    def get_parent(self, index):
+        return ((index - 1) // 2)
+
+    def get_left_child(self, index):
+        return ((index * 2) + 1)
+
+    def get_right_child(self, index):
+        return ((index * 2) + 2)
+
+    def get_smallest_child(self, index):
+        left_child = self.get_left_child(index)
+        right_child = self.get_right_child(index)
+
+        if left_child < len(self.store):
+            if right_child >= len(self.store) or (self.store[left_child].key < self.store[right_child].key):
+                smallest_child = left_child
+            else:
+                smallest_child = right_child
+            return smallest_child
 
     def add(self, key, value = None):
         """ This method adds a HeapNode instance to the heap
             If value == None the new node's value should be set to key
-            Time Complexity: ?
-            Space Complexity: ?
+            Time Complexity: O(log n)
+            Space Complexity: O(1)
         """
-        pass
+        if (value == None):
+            value = key
+
+        node = HeapNode(key, value)
+        self.store.append(node)
+        self.heap_up(len(self.store) - 1)
 
     def remove(self):
         """ This method removes and returns an element from the heap
             maintaining the heap structure
-            Time Complexity: ?
-            Space Complexity: ?
+            Time Complexity: O(log n)
+            Space Complexity: O(1)
         """
-        pass
-
-
+        if len(self.store) == 0:
+            return None
+
+        self.swap(0, len(self.store) - 1)
+        min = self.store.pop()
+        self.heap_down(0)
+        return min.value
 
     def __str__(self):
         """ This method lets you print the heap, when you're testing your app.
@@ -46,10 +72,10 @@ def __str__(self):
 
     def empty(self):
         """ This method returns true if the heap is empty
-            Time complexity: ?
-            Space complexity: ?
+            Time complexity: O(1)
+            Space complexity: O(1)
         """
-        pass
+        return len(self.store) == 0
 
 
     def heap_up(self, index):
@@ -59,19 +85,30 @@ def heap_up(self, index):
             property is reestablished.
 
             This could be **very** helpful for the add method.
-            Time complexity: ?
-            Space complexity: ?
+            Time complexity: O(log n)
+            Space complexity: O(1)
         """
-        pass
+        while index != 0:
+            node = self.store[index]
+            parent_node = self.get_parent(index)
+
+            if self.store[parent_node].key > node.key:
+                self.swap(index, parent_node)
+            index = parent_node
 
     def heap_down(self, index):
         """ This helper method takes an index and 
             moves the corresponding element down the heap if it's 
             larger than either of its children and continues until
             the heap property is reestablished.
         """
-        pass
+        if (index >= len(self.store) - 1):
+            return
+        smallest_child = self.get_smallest_child(index)
 
+        if smallest_child and self.store[index].key > self.store[smallest_child].key:
+            self.swap(index, smallest_child)
+            self.heap_down(smallest_child)
 
     def swap(self, index_1, index_2):
         """ Swaps two elements in self.store