add min heap priority queue

Author: priyankchheda

heap/minheap.py

@@ -0,0 +1,99 @@
+""" Implementation of Min Heap Data Structure """
+
+
+class MinHeap:
+    """ MinHeap is a complete binary tree.
+    In MinHeap, the key at root must be minimum among all keys
+    present in Binary Heap. The same property must be recursively true for
+    all nodes in Binary Tree.
+    """
+
+    def __init__(self):
+        """ initialize new empty 1-indexed heap """
+        self.data = [None]
+
+    def length(self):
+        """ returns total number of items present in heap """
+        return len(self.data) - 1
+
+    def is_empty(self):
+        """ checks if heap is empty or not """
+        return self.length() == 0
+
+    def insert(self, item):
+        """ inserts new item into heap while maintaining heap invariant """
+        self.data.append(item)
+        self.swim(self.length())
+
+    def get_min(self):
+        """ get_min returns the minimum value (i.e. root) in the heap,
+        without removing it. Returns None, if the heap is empty.
+        """
+        if self.is_empty():
+            return None
+        return self.data[1]
+
+    def extract_min(self):
+        """ extract_min returns the minimum value (i.e. root) in the heap
+        and removes it from the heap. Returns None, if heap is empty.
+        """
+        if self.is_empty():
+            return None
+
+        min_value = self.data[1]
+        self.data[1] = self.data[self.length()]
+        self.data = self.data[:self.length()]
+        self.sink(1)
+        return min_value
+
+    def swim(self, index):
+        """ swim moves element at index upward to maintain heap invariant """
+        if index <= 1:
+            return
+
+        parent = index // 2
+        if self.data[parent] > self.data[index]:
+            self.data[parent], self.data[index] = self.data[index], self.data[parent]
+            self.swim(parent)
+
+    def sink(self, index):
+        """ sink moves element at index downward to maintain heap invariant """
+        min_index = index
+        left = index * 2
+        right = (index * 2) + 1
+
+        if left <= self.length():
+            if self.data[min_index] > self.data[left]:
+                min_index = left
+
+        if right <= self.length():
+            if self.data[min_index] > self.data[right]:
+                min_index = right
+
+        if min_index != index:
+            self.data[index], self.data[min_index] = self.data[min_index], self.data[index]
+            self.sink(min_index)
+
+
+def main():
+    """ operational function """
+    mheap = MinHeap()
+    mheap.insert(5)
+    mheap.insert(3)
+    print(mheap.get_min())
+    mheap.insert(1)
+    mheap.insert(6)
+    mheap.insert(2)
+    print(mheap.data)
+    print(mheap.extract_min())
+    print(mheap.data)
+    print(mheap.extract_min())
+    mheap.insert(3)
+    print(mheap.extract_min())
+    print(mheap.extract_min())
+    print(mheap.extract_min())
+    print(mheap.data)
+
+
+if __name__ == "__main__":
+    main()