leetcode129

class Solution:
    def __init__(self):
        self.lists = []
        
    def preOrder(self,root,path):
        if root != None:
            path.append(str(root.val))
            if root.left != None:
                self.preOrder(root.left,path)
            if root.right != None:
                self.preOrder(root.right,path)
            
            if root.left == None and root.right == None:
                self.lists.append(path[:])
            path.pop(-1)
        
    def sumNumbers(self, root: TreeNode) -> int:
        if root == None:
            return 0
        else:
            self.preOrder(root,[])
            sums = 0
            for li in self.lists:
                s = ''.join(li)
                n = int(s)
                sums += n
            return sums