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437.py
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'''
437. Path Sum III
You are given a binary tree in which each node contains an integer value.
Find the number of paths that sum to a given value.
The path does not need to start or end at the root or a leaf, but it must
go downwards (traveling only from parent nodes to child nodes).
The tree has no more than 1,000 nodes and the values are in the range
-1,000,000 to 1,000,000.
Example:
root = [10,5,-3,3,2,null,11,3,-2,null,1], sum = 8
10
/ \
5 -3
/ \ \
3 2 11
/ \ \
3 -2 1
Return 3. The paths that sum to 8 are:
1. 5 -> 3
2. 5 -> 2 -> 1
3. -3 -> 11
'''
# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution(object):
def pathSum(self, root, sum):
"""
:type root: TreeNode
:type sum: int
:rtype: int
"""
return self.pathSumH(root, sum, [sum])
def pathSumH(self, root, sum, targets):
if not root:
return 0
count = 0
for t in targets:
if not t - root.val:
count += 1
targets = [t - root.val for t in targets] + [sum]
return count + self.pathSumH(root.left, sum, targets) + self.pathSumH(root.right, sum, targets)