404. 左叶子之和

"""
404. 左叶子之和
计算给定二叉树的所有左叶子之和。
示例：
    3
   / \
  9  20
    /  \
   15   7

在这个二叉树中，有两个左叶子，分别是 9 和 15，所以返回 24
"""
class Solution(object):
    def sumOfLeftLeaves(self, root):
        def bfs(root1):
            ans = 0
            if not root1: return
            if root1.left:
                ans += root1.left.val if self.isLeaves(root1.left) else bfs(root1.left)
            if root1.right and not self.isLeaves(root1.right):
                ans += bfs(root1.right)
            return ans
        return bfs(root)


    def isLeaves(self, root):
        if not root.left and not root.right:
            return True
        else:
            return False

class TreeNode(object):
    def __init__(self, val):
        self.val = val
        self.left = None
        self.right = None

if __name__ == "__main__":
    root = TreeNode(3)
    root.left = TreeNode(9)
    root.right = TreeNode(20)
    root.right.left = TreeNode(15)
    root.right.right = TreeNode(7)
    res = Solution().sumOfLeftLeaves(root)
    print(res)