Path Sum

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

class Solution:
# @param root, a tree node
# @param sum, an integer
# @return a boolean
def hasPathSum(self, root, sum):
ret = False
if root == None:
return ret
sum -= root.val
if sum==0 and root.left==None and root.right==None:
ret = True
return ret or self.hasPathSum(root.left,sum) or self.hasPathSum(root.right,sum)