题目：

题解：

func isLeafNode(node *TreeNode) bool {return node.Left == nil && node.Right == nil
}func sumOfLeftLeaves(root *TreeNode) (ans int) {if root == nil {return}q := []*TreeNode{root}for len(q) > 0 {node := q[0]q = q[1:]if node.Left != nil {if isLeafNode(node.Left) {ans += node.Left.Val} else {q = append(q, node.Left)}}if node.Right != nil && !isLeafNode(node.Right) {q = append(q, node.Right)}}return
}