题目描述
输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。假设输入的前序遍历和中序遍历的结果中都不含重复的数字。例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建二叉树并返回。
思路
- 用前序遍历找到根结点
- 用根结点在中序遍历中切开左右子树，递归重建二叉树
class TreeNode:
def __init__(self,x):
self.val = x
self.left = None
self.right = None
# 返回构造的TreeNode根节点
def reConstructBinaryTree(pre,tin):
if not pre:
return None
root_val = pre[0]
root = TreeNode(root_val)
for i in range(len(tin)):
if tin[i] == root.val:
break
root.left = reConstructBinaryTree(pre[1:1+i],tin[:i])
root.right = reConstructBinaryTree(pre[1+i:],tin[i+1:])
return root
def preorder(root):
if root:
preorder(root.left)
print(root.val)
preorder(root.right)
preorder(reConstructBinaryTree([1,2,3,4,5,6,7],[3,2,4,1,6,5,7])) 