树的三种遍历——递归和非递归形式的python实现_树的递归和非递归算法python

class TreeNode(object):
    #创建树的结构
    def __init__(self,x):
        self.val=x
        self.left=None
        self.right=None

#递归形式
#前序遍历
def preOrderRecusive(root):
    if root==None:
        return None
    print(root.val)
    preOrderRecusive(root.left)
    preOrderRecusive(root.right)

#中序遍历
def midOrderRecusive(root):
    if root==None:
        return None
    midOrderRecusive(root.left)
    print(root.val)
    midOrderRecusive(root.right)
#后序遍历
def lateOrderRecusive(root):
    if root==None:
        return None
    lateOrderRecusive(root.left)
    lateOrderRecusive(root.right)
    print(root.val)

#非递归形式
#前序遍历
def preOrder(root):
    if root==None:
        return None
    tmp=root
    stack=[]
    while tmp or stack:#当tmp非空或者stack非空
        while tmp:
            print(tmp.val)
            stack.append(tmp)
            tmp=tmp.left
        node=stack.pop()
        tmp=node.right#要去循环的下一个头

#中序遍历
def midOrder(root):
    if root==None:
        return None
    tmp=root
    stack=[]
    while tmp or stack:#当tmp非空或者stack非空
        while tmp:
            #print(tmp.val)
            stack.append(tmp)
            tmp=tmp.left
        node=stack.pop()
        print(node.val)
        tmp=node.right#要去循环的下一个头

#后序遍历
def lateOrder(root):
    if root==None:
        return None
    tmp=root
    stack=[]
    while tmp or stack:#当tmp非空或者stack非空
        while tmp:
            #print(tmp.val)
            stack.append(tmp)
            tmp=tmp.left
        node=stack[-1]
        tmp=node.right#要去循环的下一个头
        if node.right==None:
            node=stack.pop()
            print(node.val)
            while stack and node==stack[-1].right:
                node=stack.pop()
                print(node.val)
#创建一棵树
if __name__=='__main__':
    t1=TreeNode(1)
    t2 = TreeNode(2)
    t3 = TreeNode(3)
    t4 = TreeNode(4)
    t5 = TreeNode(5)
    t6 = TreeNode(6)
    t7 = TreeNode(7)
    t1.left=t2
    t1.right=t3
    t2.left=t4
    t2.right=t5
    t3.left=t6
    t3.right=t7
    lateOrder(t1)
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