求优化——二叉树

题目：已知某二叉树中序遍历结果为cbedahgijf、后序遍历结果为cedbhjigfa,编程实现二叉树的二叉链表示法，并输出先序遍历结果。

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

def CreateBTNode(post,im,length):
    if (length<=0):
        return None
    s=BTNode(post[-1])   
    k=-1   
    for p in im:
        k+=1
        if p==s.data:
            break
        
    s.lchild=CreateBTNode(post[0:k],im[0:k],k)
    s.rchild=CreateBTNode(post[k:length-1],im[k+1:],length-k-1)
    return s

def predis(s):
    if s!=None:
        print(s.data,end="")
        predis(s.lchild)
        predis(s.rchild)
     
   
if __name__=='__main__':
    im=input('请输入中序遍历结果：')
    post=input('请输入后序遍历结果：')
    length=len(im)   
    predis(CreateBTNode(post,im,length))
    print("")