package q102

type TreeNode struct {
	Val   int
	Left  *TreeNode
	Right *TreeNode
}

func levelOrder(root *TreeNode) [][]int {
	if root == nil {
		return [][]int{}
	}
	ret := [][]int{}

	type qElem struct {
		lvl  int
		node *TreeNode
	}
	curLvl := 0
	curLvlNodes := []int{}
	queue := []qElem{{0, root}}
	for ; len(queue) > 0; queue = queue[1:] {
		cur := &queue[0]
		if cur.lvl != curLvl {
			ret = append(ret, curLvlNodes)
			curLvlNodes = []int{cur.node.Val}
			curLvl = cur.lvl
		} else {
			curLvlNodes = append(curLvlNodes, cur.node.Val)
		}
		if cur.node.Left != nil {
			queue = append(queue, qElem{lvl: cur.lvl + 1, node: cur.node.Left})
		}
		if cur.node.Right != nil {
			queue = append(queue, qElem{lvl: cur.lvl + 1, node: cur.node.Right})
		}
	}

	ret = append(ret, curLvlNodes)
	return ret
}

var _ = levelOrder