在Python中打印二叉树插入的每个阶段的最佳方法

Question

I trying to print each stage of a Binary Search Tree after every step of Insertion. However the output generated by my code seems to miss out the initial root data insertion step and also repeats certain stages. I need a clean and easy way to do this. Is there a way to do it using __dict__.values() .

My Code:

class Node:
    def __init__(self, data):
        self.data = data
        self.left = None
        self.right = None

    def addNode(self, data):
        if data < self.data:
            if self.left is None:
                self.left = Node(data)
            else:
                self.left.addNode(data)  # recursively calling addNode method
        else:
            if self.right is None:
                self.right = Node(data)
            else:
                self.right.addNode(data)

        if not self.left is None and not self.right is None:
            print self.left.data, self.data, self.right.data
        elif self.left is None and not self.right is None:
            print None, self.data, self.right.data
        elif not self.left is None and self.right is None:
            print self.left.data, self.data, None

if __name__ == '__main__':
    n = Node(5)
    #print n.__dict__.values()
    n.addNode(3)
    n.addNode(2)
    n.addNode(8)
    n.addNode(4)

Output Generated:

3 5 None
2 3 None
3 5 None
3 5 8
2 3 4
3 5 8

Expected Output:

None 5 None
3 5 None
2 3 None
3 5 8
2 3 4

Answer 1

Because of the way you designed this, the printing step is happening on each recursive step, from the inside to the outside. So, for that to make more sense, lets walk through this. You n.addNode(3) which gives us

3 5 None

No surprises. But when you say you expect:

2 3 None

but get both,

2 3 None
3 5 None

its because to do n.addNode(2) is to examine the first level ( 3 5 None ) then to look at the lower level (the node with data attribute = 3 ). So, printing "from the inside out", we get 2 3 None (new subtree) then the first level again, 3 5 None . Its for the same reason that when you expect,

2 3 4

you instead get,

2 3 4
3 5 8

The fact that the initial tree (where you expect None 5 None ) is not printing is a separate issue. It's just because you are initializing the data attribute and don't ever get to the printing part because you don't call addNone .

A possible solution (that still maintains your structure) would be to only print when you add the node to the tree structure and print the initial subtree manually. Maybe write something like this:

class Node:
    def __init__(self, data):
        self.data = data
        self.left = None
        self.right = None

    def addNode(self, data):
        if data < self.data:
            if self.left is None:
                self.left = Node(data)
                self.printSubtree()
            else:
                self.left.addNode(data)  # recursively calling addNode method
        else:
            if self.right is None:
                self.right = Node(data)
                self.printSubtree()
            else:
                self.right.addNode(data)

    def printSubtree(self):
        if not self.left is None and not self.right is None:
            print self.left.data, self.data, self.right.data
        elif self.left is None and not self.right is None:
            print None, self.data, self.right.data
        elif not self.left is None and self.right is None:
            print self.left.data, self.data, None
        else:
            print None, self.data, None

if __name__ == '__main__':
    n = Node(5)
    n.printSubtree()
    n.addNode(3)
    n.addNode(2)
    n.addNode(8)
    n.addNode(4)

Answer 2

1- you printed after adding the nodes, so you can't find an element with None,Number,None as you expect.(so try to move this part before adding the node). 2- when printing you only considered three possibilities but there is another one, when the left and the right nodes are both None, try adding this.