[LC] 112. Path Sum

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

Note: A leaf is a node with no children.

Example:

Given the below binary tree and sum = 22,

      5
     / 
    4   8
   /   / 
  11  13  4
 /        
7    2      1

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

 1 # Definition for a binary tree node.
 2 # class TreeNode:
 3 #     def __init__(self, x):
 4 #         self.val = x
 5 #         self.left = None
 6 #         self.right = None
 7 
 8 class Solution:
 9     def hasPathSum(self, root: TreeNode, sum: int) -> bool:
10         res = self.helper(root, sum)
11         return res
12     
13     def helper(self, root, sum):
14         if root is None:
15             return False
16         if root.left is None and root.right is None:
17             if sum == root.val:
18                 return True
19             else:
20                 return False
21         left = self.helper(root.left, sum - root.val)
22         right = self.helper(root.right, sum - root.val)
23         return left or right