题:https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/description/
题目
Given preorder and inorder traversal of a tree, construct the binary tree.
Note:
You may assume that duplicates do not exist in the tree.
For example, given
preorder = [3,9,20,15,7]
inorder = [9,3,15,20,7]
Return the following binary tree:
3
/ \
9 20
/ \
15 7
思路
递归,建树。
还需要改进
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
def tbuild(preorder,inorder,pstart,pend,istart,iend):
if pstart >= pend:
return None
node = TreeNode(preorder[pstart])
for i in range(istart,iend):
if inorder[i] == node.val:
break
print(preorder[pstart])
node.left = tbuild(preorder,inorder,pstart + 1,pstart+(i - istart)+1,istart,i)
node.right = tbuild(preorder,inorder,pstart+(i - istart)+1,pend,i+1,iend)
return node
class Solution:
def buildTree(self, preorder, inorder):
"""
:type preorder: List[int]
:type inorder: List[int]
:rtype: TreeNode
"""
return tbuild(preorder, inorder,0,len(preorder),0,len(inorder))