Create radixsort.py

radixsort.py

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+# Implementation of the Queue ADT using a linked list.
+class lQueue :
+
+  # Creates an empty queue.
+  def __init__( self ):
+    self._qhead = None 
+    self._qtail = None 
+    self._count = 0
+
+  # Returns True if the queue is empty.
+  def isEmpty( self ):
+    return self._qhead is None
+
+  # Returns the number of items in the queue.
+  def __len__( self ):
+    return self._count
+
+  # Adds the given item to the queue.
+  def enqueue( self, item ):
+    node = _QueueNode( item ) 
+
+    if self.isEmpty() :
+      self._qhead = node 
+    else :
+      self._qtail.next = node
+
+    self._qtail = node
+    self._count += 1
+
+  # Removes and returns the first item in the queue.
+  def dequeue( self ):
+    assert not self.isEmpty(), "Cannot dequeue from an empty queue." 
+    node = self._qhead
+
+    if self._qhead is self._qtail :
+      self._qtail = None
+
+    self._qhead = self._qhead.next 
+    self._count -= 1
+    return node.item
+
+  # Private storage class for creating the linked list nodes.
+class _QueueNode( object ):
+  def __init__( self, item ):
+    self.item = item
+    self.next = None
+
+#### Sorts a sequence of positive integers using the radix sort algorithm.
+
+def radixSort( intList, numDigits ):
+
+    # Create a list of queues to represent the bins.
+    binArray = [-1]*10 
+    for k in range( 10 ):
+        binArray[k] = lQueue()
+
+    # The value of the current column.
+    column = 1
+
+    # Iterate over the number of digits in the largest value.
+    for d in range( numDigits ):
+        # Distribute the keys across the 10 bins.
+        for key in intList :
+            digit = (key // column) % 10 
+            binArray[digit].enqueue( key )
+
+        # Gather the keys from the bins and place them back in intList.
+        i=0
+        for bin in binArray :
+            while not bin.isEmpty() : 
+                intList[i] = bin.dequeue() 
+                i += 1
+         # Advance to the next column value.
+        column *= 10
+
+    return(intList)