golang力扣leetcode 107. 二叉树的层序遍历 II

package main
func main() {
}
type TreeNode struct {
  Val   int
  Left  *TreeNode
  Right *TreeNode
}
func levelOrderBottom(root *TreeNode) [][]int {
  result := levelOrder(root)
  return reverse(result)
}
func reverse(cnt [][]int) [][]int {
  for i, j := 0, len(cnt)-1; i < j; i, j = i+1, j-1 {
    cnt[i], cnt[j] = cnt[j], cnt[i]
  }
  return cnt
}
func levelOrder(root *TreeNode) [][]int {
  if root == nil {
    return nil
  }
  result := make([][]int, 0)
  queue := make([]*TreeNode, 0)
  queue = append(queue, root)
  for len(queue) > 0 {
    cnt := make([]int, 0)
    queueSize := len(queue)
    for i := 0; i < queueSize; i++ {
      //出队
      v := queue[0]
      queue = queue[1:]
      //入队
      if v.Left != nil {
        queue = append(queue, v.Left)
      }
      if v.Right != nil {
        queue = append(queue, v.Right)
      }
      cnt = append(cnt, v.Val)
    }
    result = append(result, cnt)
  }
  return result
}