Merge pull request #169 from jerryderry/heap-python

max-heap in python

python/28_heap/heap.py

@@ -0,0 +1,96 @@
+"""
+    Max-heap
+
+    Author: Wenru Dong
+"""
+
+from typing import Optional, List
+
+class Heap:
+    def __init__(self, capacity: int):
+        self._data = [0] * (capacity + 1)
+        self._capacity = capacity
+        self._count = 0
+    
+    @classmethod
+    def _parent(cls, child_index: int) -> int:
+        """The parent index."""
+        return child_index // 2
+    
+    @classmethod
+    def _left(cls, parent_index: int) -> int:
+        """The left child index."""
+        return 2 * parent_index
+    
+    @classmethod
+    def _right(cls, parent_index: int) -> int:
+        """The right child index."""
+        return 2 * parent_index + 1
+
+    def _siftup(self) -> None:
+        i, parent = self._count, Heap._parent(self._count)
+        while parent and self._data[i] > self._data[parent]:
+            self._data[i], self._data[parent] = self._data[parent], self._data[i]
+            i, parent = parent, Heap._parent(parent)
+
+    @classmethod
+    def _siftdown(cls, a: List[int], count: int, root_index: int = 1) -> None:
+        i = larger_child_index = root_index
+        while True:
+            left, right = cls._left(i), cls._right(i)
+            if left <= count and a[i] < a[left]:
+                larger_child_index = left
+            if right <= count and a[larger_child_index] < a[right]:
+                larger_child_index = right
+            if larger_child_index == i: break
+            a[i], a[larger_child_index] = a[larger_child_index], a[i]
+            i = larger_child_index
+
+    def insert(self, value: int) -> None:
+        if self._count >= self._capacity: return
+        self._count += 1
+        self._data[self._count] = value
+        self._siftup()
+
+    def remove_max(self) -> Optional[int]:
+        if self._count:
+            result = self._data[1]
+            self._data[1] = self._data[self._count]
+            self._count -= 1
+            Heap._siftdown(self._data, self._count)
+            return result
+
+    @classmethod
+    def build_heap(cls, a: List[int]) -> None:
+        """Data in a needs to start from index 1."""
+        for i in range((len(a) - 1)//2, 0, -1):
+            cls._siftdown(a, len(a) - 1, i)
+    
+    @classmethod
+    def sort(cls, a: List[int]) -> None:
+        """Data in a needs to start from index 1."""
+        cls.build_heap(a)
+        k = len(a) - 1
+        while k > 1:
+            a[1], a[k] = a[k], a[1]
+            k -= 1
+            cls._siftdown(a, k)
+
+    def __repr__(self):
+        return self._data[1 : self._count + 1].__repr__()
+
+
+if __name__ == "__main__":
+    hp = Heap(10)
+    hp.insert(3)
+    hp.insert(9)
+    hp.insert(1)
+    hp.insert(8)
+    hp.insert(7)
+    hp.insert(3)
+    print(hp)
+    for _ in range(6):
+        print(hp.remove_max())
+    a = [0, 6, 3, 4, 0, 9, 2, 7, 5, -2, 8, 1, 6, 10]
+    Heap.sort(a)
+    print(a[1:])