题目：
题解：
func levelOrderBottom(root *TreeNode) [][]int {levelOrder := [][]int{}if root == nil {return levelOrder}queue := []*TreeNode{}queue = append(queue, root)for len(queue) > 0 {level := []int{}size := len(queue)for i := 0; i < size; i++ {node := queue[0]queue = queue[1:]level = append(level, node.Val)if node.Left != nil {queue = append(queue, node.Left)}if node.Right != nil {queue = append(queue, node.Right)}}levelOrder = append(levelOrder, level)}for i := 0; i < len(levelOrder) / 2; i++ {levelOrder[i], levelOrder[len(levelOrder) - 1 - i] = levelOrder[len(levelOrder) - 1 - i], levelOrder[i]}return levelOrder
}
