105. Construct Binary Tree from Preorder and Inorder Traversal (Medium) - TengnanYao/daily_leetcode GitHub Wiki

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
    def buildTree(self, preorder, inorder):
        """
        :type preorder: List[int]
        :type inorder: List[int]
        :rtype: TreeNode
        """
        # recursion
        if inorder:
            root = TreeNode(preorder[0])
            i = inorder.index(preorder.pop(0))
            root.left = self.buildTree(preorder, inorder[ : i])
            root.right = self.buildTree(preorder, inorder[i + 1 : ])
            return root
        
        # # iteration
        # h = {}
        # for i, num in enumerate(inorder):
        #     h[num] = i
        # root = cur = TreeNode(preorder[0])
        # for i, num in enumerate(preorder[1 : ]):
        #     while True:
        #         if h[cur.val] > h[num]:
        #             if cur.left:
        #                 cur = cur.left
        #             else:
        #                 cur.left = TreeNode(num)
        #                 cur = root
        #                 break
        #         elif h[cur.val] < h[num]:
        #             if cur.right:
        #                 cur = cur.right
        #             else:
        #                 cur.right = TreeNode(num)
        #                 cur = root
        #                 break
        # return root