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BM40A1500 Data Structures and Algorithms/Assignments/Week 6/minheap.py

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+class MinHeap:
+    def __init__(self):
+        self.heap = []
+
+    def push(self, key):
+        self.heap.append(key)
+        self.bubble_up(len(self.heap) - 1)
+
+    def bubble_up(self, index):
+        if index == 0:
+            return
+        parent = (index - 1) // 2
+        if self.heap[parent] > self.heap[index]:
+            self.heap[parent], self.heap[index] = self.heap[index], self.heap[parent]
+            self.bubble_up(parent)
+
+    def pop(self):
+        if len(self.heap) == 0:
+            return None
+        if len(self.heap) == 1:
+            return self.heap.pop()
+        self.heap[0], self.heap[-1] = self.heap[-1], self.heap[0]
+        min = self.heap.pop()
+        self.bubble_down(0)
+        return min
+
+    def bubble_down(self, index):
+        left = 2 * index + 1
+        right = 2 * index + 2
+        smallest = index
+        if left < len(self.heap) and self.heap[left] < self.heap[smallest]:
+            smallest = left
+        if right < len(self.heap) and self.heap[right] < self.heap[smallest]:
+            smallest = right
+        if smallest != index:
+            self.heap[smallest], self.heap[index] = self.heap[index], self.heap[smallest]
+            self.bubble_down(smallest)
+
+    def print(self):
+        print(' '.join(map(str, self.heap)))
+
+
+if __name__ == "__main__":
+    items = [4, 8, 6, 5, 1, 2, 3]
+    heap = MinHeap()
+    [heap.push(key) for key in items]
+    heap.print()        # 1 4 2 8 5 6 3
+    print(heap.pop())   # 1
+    heap.print()        # 2 4 3 8 5 6