404 sum of left leaves
404. Sum of Left Leaves
题目: https://leetcode.com/problems/sum-of-left-leaves/
难度: Easy
思路：
典型递归，检查root的左孩子是不是node，是的话加上它的值，不是的话递归去求它的孩子们的，对于右边，递归的求sum of left leaves
class Solution(object):
def sumOfLeftLeaves(self, root):
"""
:type root: TreeNode
:rtype: int
"""
def isLeaf(node):
if node == None:
return False
if node.left == None and node.right == None:
return True
return False
res = 0
if root:
if isLeaf(root.left):
res += root.left.val
else:
res += self.sumOfLeftLeaves(root.left)
if root.right:
res += self.sumOfLeftLeaves(root.right)
return res
