二叉树前序遍历&后续遍历&中序遍历

class BiTNode():
    def __init__(self):
        self.data = None
        self.lchild = None
        self.rchild = None

# 方法功能：把有序数组转为二叉树
def arraytotree(arr,start,end):
    root = None
    if end >= start:
        root = BiTNode()
        mid = (start+end+1)//2
        # 树的根节点为数组中间的元素
        root.data = arr[mid]
        print(root.data)
        # 递归的用左半部分数组构成 root 的左子树
        root.lchild = arraytotree(arr,start,mid-1)
        # 递归地用右半部分数组构成 root 的右子树
        root.rchild = arraytotree(arr,mid+1,end)
    else:
        root = None
    return root

# 用中序遍历的方法打印出二叉树结点的内容
def printTreeMidOrder(root):
    if root == None:
        return None
    #遍历root结点的左子树
    if root.lchild != None:
        printTreeMidOrder(root.lchild)
    #遍历root结点
    print(root.data,end=' ')   #先从左边遍历
    #遍历 root 的右子树
    if root.rchild != None:
        printTreeMidOrder(root.rchild)

#前序遍历
def printTreePreOrder(root):
    if root == None:
        return None
    #遍历root结点
    print(root.data,end=' ')
    #遍历root结点的左子树
    if root.lchild != None:
        printTreeMidOrder(root.lchild)
    #遍历 root 的右子树
    if root.rchild != None:
        printTreeMidOrder(root.rchild)

#后序遍历
def printTreeAfterOrder(root):
    if root == None:
        return None
    #遍历root结点的左子树
    if root.lchild != None:
        printTreeMidOrder(root.lchild)
    #遍历 root 的右子树
    if root.rchild != None:
        printTreeMidOrder(root.rchild)
    #遍历root结点
    print(root.data,end=' ')   

arr = [1,2,3,4,5,6,7,8,9,10]
print("数组：",end='')
i = 0
while i < len(arr):
    print(arr[i],end = ' ')
    i += 1
print()
root = arraytotree(arr,0,len(arr)-1)
print("转换成树的中序遍历为：",end='')
printTreeMidOrder(root)