题解 | #二叉树中是否存在节点和为指定值的路径#

helper 函数：以root根的结点，是否存在到叶子结点使得pathsum为s

# 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 ):
        # write code here
        def helper(root, s):
            if not root:
                return False
            elif not root.left and not root.right and s == root.val:
                return True
            else:
                return helper(root.left, s-root.val) or helper(root.right, s-root.val)
        return helper(root, sum)