I wrote a code for the leetcode problem "108. Sum of Left Leaves" using recursion. It didn't give me the expected result.
# 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 sumOfLeftLeaves(self, root): """ :type root: TreeNode :rtype: int """ if root is None: return 0 ans = 0 if root.left and not root.left.left and not root.left.right: ans += root.left.val self.sumOfLeftLeaves(root.left) self.sumOfLeftLeaves(root.right) return ans When the input is [3,9,20,null,null,15,7]
I expected a 24 to be returned, but the code only gave me 9
1 Answer
You aren't adding the results of the leaves below the root. You need this:
class Solution(object): def sumOfLeftLeaves(self, root): """ :type root: TreeNode :rtype: int """ if root is None: return 0 ans = 0 if root.left and not root.left.left and not root.left.right: ans += root.left.val ans += self.sumOfLeftLeaves(root.left) + self.sumOfLeftLeaves(root.right) return ans 
