Family Day update

Task/Tree-traversal/Python/tree-traversal-1.py

@@ -1,5 +1,4 @@
 from collections import namedtuple
-from sys import stdout
 
 Node = namedtuple('Node', 'data, left, right')
 tree = Node(1,
@@ -15,41 +14,59 @@ tree = Node(1,
                  None))
 
 def printwithspace(i):
-    stdout.write("%i " % i)
+    print(i, end=' ')
+
+def dfs(order, node, visitor):
+    if node is not None:
+        for action in order:
+            if action == 'N':
+                visitor(node.data)
+            elif action == 'L':
+                dfs(order, node.left, visitor)
+            elif action == 'R':
+                dfs(order, node.right, visitor)
 
 def preorder(node, visitor = printwithspace):
-    if node is not None:
-        visitor(node.data)
-        preorder(node.left, visitor)
-        preorder(node.right, visitor)
+    dfs('NLR', node, visitor)
 
 def inorder(node, visitor = printwithspace):
-    if node is not None:
-        inorder(node.left, visitor)
-        visitor(node.data)
-        inorder(node.right, visitor)
+    dfs('LNR', node, visitor)
 
 def postorder(node, visitor = printwithspace):
-    if node is not None:
-        postorder(node.left, visitor)
-        postorder(node.right, visitor)
-        visitor(node.data)
+    dfs('LRN', node, visitor)
 
-def levelorder(node, more=None, visitor = printwithspace):
-    if node is not None:
+def ls(node, more, visitor, order='TB'):
+    "Level-based Top-to-Bottom or Bottom-to-Top tree search"
+    if node:
         if more is None:
             more = []
         more += [node.left, node.right]
-        visitor(node.data)
-    if more:
-        levelorder(more[0], more[1:], visitor)
+    for action in order:
+        if action == 'B' and more:
+            ls(more[0], more[1:], visitor, order)
+        elif action == 'T' and node:
+            visitor(node.data)
 
-stdout.write('  preorder: ')
-preorder(tree)
-stdout.write('\n   inorder: ')
-inorder(tree)
-stdout.write('\n postorder: ')
-postorder(tree)
-stdout.write('\nlevelorder: ')
-levelorder(tree)
-stdout.write('\n')
+def levelorder(node, more=None, visitor = printwithspace):
+    ls(node, more, visitor, 'TB')
+
+# Because we can
+def reverse_preorder(node, visitor = printwithspace):
+    dfs('RLN', node, visitor)
+
+def bottom_up_order(node, more=None, visitor = printwithspace, order='BT'):
+    ls(node, more, visitor, 'BT')
+
+
+if __name__ == '__main__':
+    w = 10
+    for traversal in [preorder, inorder, postorder, levelorder,
+                      reverse_preorder, bottom_up_order]:
+        if traversal == reverse_preorder:
+            w = 20
+            print('\nThe generalisation of function dfs allows:')
+        if traversal == bottom_up_order:
+            print('The generalisation of function ls allows:')
+        print(f"{traversal.__name__:>{w}}:", end=' ')
+        traversal(tree)
+        print()