Leetcode 437. Path Sum III

进入pathSum函数后有两种情况,一种是包括root的值一种是不包括.

# 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 __init__(self):
        self.ans=0
        
    def pathSum(self, root, sum):
        """
        :type root: TreeNode
        :type sum: int
        :rtype: int
        """
        if not root:
            return 0
        
        self.pathSumWithNode(root,sum)
        self.pathSum(root.left,sum)
        self.pathSum(root.right,sum)
        
        return self.ans
    def pathSumWithNode(self,root,sum):
        if not root:
            return 0
        if root.val==sum:
            self.ans+=1
        self.pathSumWithNode(root.left,sum-root.val)
        self.pathSumWithNode(root.right,sum-root.val)