path sum ii

# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class (object):
    def pathSum(self, root, sum):
        """
        :type root: TreeNode
        :type sum: int
        :rtype: List[List[int]]
        """
        ret = []
        self.helper(root, [], sum, ret)
        return ret
    
    def helper(self, root, cur, sum, ret):
        if not root:
            return
        if not root.left and not root.right and sum - root.val == 0:
            cur.append(root.val)
            ret.append(cur[:])
            cur.pop()
            return
        for node in [root.left, root.right]:
            sum -= root.val
            cur.append(root.val)
            self.helper(node, cur, sum, ret)
            sum += root.val
            cur.pop()