Add min heap challenge

graphs_trees/min_heap/min_heap.py

@@ -0,0 +1,66 @@
+from __future__ import division
+
+import sys
+
+
+class MinHeap(object):
+
+    def __init__(self):
+        self.array = []
+
+    def __len__(self):
+        return len(self.array)
+
+    def extract_min(self):
+        if not self.array:
+            return None
+        if len(self.array) == 1:
+            return self.array.pop(0)
+        minimum = self.array[0]
+        # Move the last element to the root
+        self.array[0] = self.array.pop(-1)
+        self._bubble_down(index=0)
+        return minimum
+
+    def peek_min(self):
+        return self.array[0] if self.array else None
+
+    def insert(self, key):
+        if key is None:
+            raise TypeError('key cannot be None')
+        self.array.append(key)
+        self._bubble_up(index=len(self.array)-1)
+
+    def _bubble_up(self, index):
+        if index == 0:
+            return
+        index_parent = (index-1) // 2
+        if self.array[index] < self.array[index_parent]:
+            # Swap the indices and recurse
+            self.array[index], self.array[index_parent] = \
+                self.array[index_parent], self.array[index]
+            self._bubble_up(index_parent)
+
+    def _bubble_down(self, index):
+        min_child_index = self._find_smaller_child(index)
+        if min_child_index == -1:
+            return
+        if self.array[index] > self.array[min_child_index]:
+            # Swap the indices and recurse
+            self.array[index], self.array[min_child_index] = \
+                self.array[min_child_index], self.array[index]
+            self._bubble_down(min_child_index)
+
+    def _find_smaller_child(self, index):
+        left_child_index = 2 * index + 1
+        right_child_index = 2 * index + 2
+        if right_child_index >= len(self.array):
+            if left_child_index >= len(self.array):
+                return -1
+            else:
+                return left_child_index
+        else:
+            if self.array[left_child_index] < self.array[right_child_index]:
+                return left_child_index
+            else:
+                return right_child_index