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)