PU Path Sum II

              5
             / 
            4   8
           /   / 
          11  13  4
         /      / 
        7    2  5   1

[
   [5,4,11,2],
   [5,8,4,5]
]

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def pathSum(self, root, sum):
        """
        :type root: TreeNode
        :type sum: int
        :rtype: List[List[int]]
        """
        if not root: return []
        cur = []
        res = []
        def preorder(root, sum):
            cur.append(root.val)
            if not root.left and not root.right and sum == root.val:
                res.append(cur[:])
            if root.left: preorder(root.left, sum - root.val)
            if root.right: preorder(root.right, sum - root.val)
            cur.pop()
        preorder(root, sum)
        return res