# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
 
class Solution:
    # @param inorder, a list of integers
    # @param postorder, a list of integers
    # @return a tree node
    def buildTree(self, inorder, postorder):
        if not inorder: return None # inorder is empty
        self.inorder, self.postorder = inorder, postorder
        return self.dfs(0, 0, len(inorder))
    
    def dfs(self, inLeft, postLeft, Len):
        if Len <= 0:
            return None
        root = TreeNode(self.postorder[postLeft + Len - 1])
        rootPos = self.inorder.index(self.postorder[postLeft + Len - 1])
        root.left = self.dfs(inLeft, postLeft, rootPos - inLeft)
        root.right = self.dfs(rootPos + 1, postLeft + rootPos - inLeft, Len - 1 - (rootPos - inLeft))
        return root