# 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: Optional[TreeNode], targetSum: int) -> int:
count =0
def dfs(node, just_started, sub_sum):
nonlocal count
if node == None:
return 0
sub_sum += node.val
if sub_sum == targetSum:
count +=1
if node.left:
dfs(node.left, False, sub_sum)
if node.right:
dfs(node.right, False, sub_sum)
if just_started:
if node.left:
dfs(node.left, True, 0)
if node.right:
dfs(node.right, True, 0)
dfs(root, True, 0)
return count
https://youtu.be/euUkM71eD6U?si=j3Mfu0twXdg30_ar
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