JZ22 从上往下打印二叉树

func PrintFromTopToBottom( root *TreeNode ) []int {
    if root == nil {
        return []int{}
    }
    queue := []*TreeNode{root}
    var res []int
    var node *TreeNode
    for i := 0; i < len(queue);i++ {  
        node = queue[i]
        res = append(res, node.Val)
        if node.Left != nil {
            queue = append(queue, node.Left)
        }
        if node.Right != nil {
            queue = append(queue, node.Right)
        }
    }
    return res
}