Python每日一题——PAT甲级1020 Tree Traversals

题目

由后序序列和中序序列得到层序序列

思路

1.由由后序序列和中序序列建树
2.得到树的层序序列

Python代码

n = int(input())
post = list(map(int,input().split()))
inorder = list(map(int,input().split()))
class node:
    def __init__(self,val,left=None,right=None):
        self.val=val
        self.left=left
        self.right=right
class Tree:
    def __init__(self,root):
        self.root=root
    def levelorder(self):
        ret=[]
        t=self.root
        if t==None:return ret
        queue = [t]
        while queue != []:
            l=len(queue)
            for i in range(l):
                p=queue.pop(0)
                ret.append(p.val)
                if p.left != None:queue.append(p.left)
                if p.right != None:queue.append(p.right)
        return ret
def Create(post,ins):
    root = _Create(post,0,ins,0,n)
    bt=Tree(root)
    return bt

def _Create(post,i,ins,j,n):
    if n<=0:return None
    val=post[i+n-1]
    root = node(val)
    r = ins.index(val) #根节点索引
    k=r-j #当前根节点的左子树节点数
    root.left=_Create(post,i,ins,j,k)
    root.right=_Create(post,i+k,ins,r+1,n-k-1)
    return root

bt = Create(post,inorder)
ret = bt.levelorder()
print(*ret)