404._sum_of_left_leaves.md

###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