動機
複習inorder與preorder
可以順便看106
Problem
Given two integer arrays preorder
and inorder
where preorder
is the preorder traversal of a binary tree and inorder
is the inorder traversal of the same tree, construct and return the binary tree.
Example 1:
Input: preorder = [3,9,20,15,7], inorder = [9,3,15,20,7]Output: [3,9,20,null,null,15,7]
Example 2:
Input: preorder = [-1], inorder = [-1]Output: [-1]
Constraints:
1 <= preorder.length <= 3000
inorder.length == preorder.length
-3000 <= preorder[i], inorder[i] <= 3000
preorder
andinorder
consist of unique values.- Each value of
inorder
also appears inpreorder
. preorder
is guaranteed to be the preorder traversal of the tree.inorder
is guaranteed to be the inorder traversal of the tree.
Sol
python的list slice好讚
class Solution:
def buildTree(self, pre: List[int], ino: List[int]) -> TreeNode:
if not ino or not pre:
return None
elif pre[0] in ino:
i = ino.index(pre[0])
ret = TreeNode(pre[0])
ret.left, ret.right = [self.buildTree(pre[1:], ino[:i]), self.buildTree(pre[1:],ino[i+1:])]
return ret
else:
return self.buildTree(pre[1:],ino)