437. Path Sum III - LeetCode Solution

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def pathSum(self, root: TreeNode, target_sum: int) -> int:
        
        
        def dfs(node: TreeNode, sum: List[int]) -> int:
            if not node:
                return 0
            sum = [s + node.val for s in sum] + [node.val]
            res = sum.count(target_sum)
            res += dfs(node.left, sum) if node.left else 0
            res += dfs(node.right, sum) if node.right else 0
            return res
        return dfs(root, [])