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// @Title: 从上到下打印二叉树 II (从上到下打印二叉树 II LCOF)
// @Author: 15816537946@163.com
// @Date: 2022-02-10 23:55:38
// @Runtime: 0 ms
// @Memory: 2.6 MB
func levelOrder(root *TreeNode) [][]int {
    var res [][]int
    if root == nil {
        return res
    }

    queue:= []*TreeNode{root}
    for len(queue) != 0 {
        curlLevel := make([]int,0)
        size := len(queue)

        for i:=0;i<size;i++ {
            node := queue[0]
            queue = queue[1:]
            if node != nil {
                curlLevel = append(curlLevel,node.Val)
            }
            if node.Left != nil {
                queue = append(queue, node.Left)
            }
            if node.Right != nil {
                queue = append(queue,node.Right)
            }
        }

        res = append(res, curlLevel)
    }

    return res
}