[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.

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

class Solution:
    def hasPathSum(self, root: TreeNode, sum: int) -> bool:
        res = self.helper(root, sum)
        return res
    
    def helper(self, root, sum):
        if root is None:
            return False
        if root.left is None and root.right is None:
            if sum == root.val:
                return True
            else:
                return False
        left = self.helper(root.left, sum - root.val)
        right = self.helper(root.right, sum - root.val)
        return left or right