二叉树的前序、中序、后序遍历的非递归方法 python

时间:2021-12-17 11:25:08
class TreeNode:
    def __init__(self,value=None,leftNode=None,rightNode=None):
        self.value = value
        self.leftNode = leftNode
        self.rightNode = rightNode


class Tree:
    def __init__(self,root=None):
        self.root = root

    def preOrder(self):
        if not self.root:
            return
        stackNode = []
        stackNode.append(self.root)
        while stackNode:
            node = stackNode.pop()
            print node.value,
            if node.rightNode:
                stackNode.append(node.rightNode)
            if node.leftNode:
                stackNode.append(node.leftNode)

    def midOrder(self):
        if not self.root:
            return
        stackNode = []
        node = None
        node = self.root
        while stackNode or node:
            while node:
                stackNode.append(node)
                node = node.leftNode
            node = stackNode.pop()
            print node.value,
            node = node.rightNode

    def aftOrder(self):
        if not self.root:
            return
        stackNode = []
        markNode = None
        node = self.root
        while stackNode or node:
           while node:
            stackNode.append(node)
            node = node.leftNode
           node = stackNode.pop()
           if not node.rightNode or node.rightNode is markNode:
            #node  has no rightNode or node's rightNode has been checked
            print node.value,
            markNode = node
            node = None
           else:
            stackNode.append(node)
            node = node.rightNode

##    #another solution to the middleOrder
##    def midOrder(self):
##        if not self.root:
##            return
##        stackNode = []
##        stackNode.append(self.root)
##        while stackNode:
##            node = stackNode.pop()
##            if node:
##                stackNode.append(node)
##                node = node.leftNode
##                stackNode.append(node)
##            elif stackNode:
##                node = stackNode.pop()
##                print node.value,
##                stackNode.append(node.rightNode)

if __name__ is '__main__':
    n10 = TreeNode(10,0,0)
    n9 = TreeNode(9,0,0)
    n3 = TreeNode(3,n9,n10)
    n8 = TreeNode(8,0,0)
    n14 = TreeNode(14,0,0)
    n7 = TreeNode(7,0,0)
    n16 = TreeNode(16,n7,0)
    n2 = TreeNode(2,n14,n8)
    n1 = TreeNode(1,n2,n16)
    root = TreeNode(4,n1,n3)
    tree = Tree(root)

    tree.midOrder()