python递归

递归先序遍历
判断当前节点是否为空，递归退出条件
判断条件：叶子节点+和等于sum，返回真，否则返回左子树和右子树的或结果；

# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

#
# 
# @param root TreeNode类 
# @param sum int整型 
# @return bool布尔型
#
class Solution:
    def hasPathSum(self , root , sum ):
        def pre_order(root,res):
            if not root:return False

            res+=root.val
            if not root.left and not root.right and res==sum:
                return True
            return pre_order(root.left, res) or pre_order(root.right, res)
        return False if not root else pre_order(root,0)