BEGIN:

class TreeNode:
    '''
    樹節點
    '''
    def __init__(self,x):
        self.val = x
        self.left = None
        self.right = None

def preTraversal(head):
    '''
    先根遍歷
    :param head: 
    :return: 
    '''
    if not head:
        return
    print(head.val)
    preTraversal(head.left)
    preTraversal(head.right)

 
def midTraversal(head):
    '''
    中跟遍歷
    :param head: 
    :return: 
    '''
    if not head:
        return
    midTraversal(head.left)
    print(head.val)
    midTraversal(head.right)

def postTraversal(head):
    '''
    後根遍歷
    :param head: 
    :return: 
    '''
    if not head:
        return
 

    postTraversal(head.left)
    postTraversal(head.right)
    print(head.val)


"""
樹結構：
                                        A
                                 B              C
                             D      E       F       G      
先跟遍歷：ABDECFG
中跟遍歷：DBEAFCG
後根遍歷：DEBFGCA
"""
A, B, C, D, E, F, G, H, I, J, K, L ,M ,N 
 
= [TreeNode(x) for x in 'abcdefghijklmn']
A.left = B
A.right = C
B.left = D
B.right = E
C.left = F
C.right = G
head = A

print("preTraversal>>>")
preTraversal(head)
print("midTraversal>>>")
midTraversal(head)
print("postTraversal>>>")
postTraversal(head)

END.