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// @Title: 从上到下打印二叉树 (从上到下打印二叉树 LCOF)
// @Author: 15816537946@163.com
// @Date: 2022-02-10 22:24:48
// @Runtime: 0 ms
// @Memory: 2.5 MB
func levelOrder(root *TreeNode) []int {
	ret := make([]int,0)
	records := []*TreeNode{root}
	var cnt int
	for records[len(records)-1] != nil {
        //fmt.Println(ret)
		v := records[cnt]
		records[cnt] = nil
		if v != nil {
			ret = append(ret, v.Val)
		} else {
            continue
        }
		if v.Left != nil {
			records = append(records,v.Left)
		}
		if v.Right != nil {
			records = append(records, v.Right)
		}

        cnt++
	}

	return ret
}