path sum

# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class (object):
    def hasPathSum(self, root, sum):
        """
        :type root: TreeNode
        :type sum: int
        :rtype: bool
        """
        return self.helper(root, 0, sum)
    
    def helper(self, root, cur, sum):
        if not root:
            return False
        cur += root.val
        if not root.left and not root.right and cur == sum:
            return True
        return self.helper(root.left, cur, sum) or self.helper(root.right, cur, sum)