Create huffman.py

other/huffman.py

@@ -0,0 +1,77 @@
+import heapq
+import itertools
+
+'''
+    heapq library of python - https://docs.python.org/2/library/heapq.html
+'''
+
+pq = []                         # list of entries arranged in a heap
+entry_finder = {}               # mapping of tasks to entries
+REMOVED = '<removed-task>'      # placeholder for a removed task
+counter = itertools.count()     # unique sequence count
+
+def add_task(task, priority=0):
+    'Add a new task or update the priority of an existing task'
+    if task in entry_finder:
+        remove_task(task)
+    count = next(counter)
+    entry = [priority, count, task]
+    entry_finder[task] = entry
+    heapq.heappush(pq, entry)
+
+def remove_task(task):
+    'Mark an existing task as REMOVED.  Raise KeyError if not found.'
+    entry = entry_finder.pop(task)
+    entry[-1] = REMOVED
+
+def pop_task():
+    'Remove and return the lowest priority task. Raise KeyError if empty.'
+    while pq:
+        priority, count, task = heapq.heappop(pq)
+        if task is not REMOVED:
+            del entry_finder[task]
+            return task
+    raise KeyError('pop from an empty priority queue')
+
+def inorder(root):
+    if(root != None):
+        inorder(root.left)
+        print(root.frequency)
+        inorder(root.right)
+
+class Node():
+    def __init__(self, d, f):
+        self.data = d
+        self.frequency = f
+        self.left = None
+        self.right = None
+
+def greedy_huffman():
+    while(len(pq) > 1):
+        left = pop_task()
+        right = pop_task()
+        freq = left.frequency + right.frequency
+        z = Node(None, freq)
+        z.left = left
+        z.right = right
+        add_task(z, z.frequency)
+
+    return pop_task()
+
+if __name__ == '__main__':
+    a = Node('a', 42)
+    b = Node('b', 20)
+    c = Node('c', 5)
+    d = Node('d', 10)
+    e = Node('e', 11)
+    f = Node('f', 12)
+
+    add_task(a, a.frequency)
+    add_task(b, b.frequency)
+    add_task(c, c.frequency)
+    add_task(d, d.frequency)
+    add_task(e, e.frequency)
+    add_task(f, f.frequency)
+
+    tree = greedy_huffman()
+    inorder(tree)