剑指 Offer 32 - I. 从上到下打印二叉树

剑指 Offer 32 - II. 从上到下打印二叉树 II

和力扣102. 二叉树的层序遍历，107. 二叉树的层序遍历 II类似

  1. //BFS    分层打印【【1】，【2，3】】
  2. func levelOrder(root *TreeNode) [][]int {
  3.     if root == nil {
  4.         return nil
  5.     }
  7.     levels := [][]int{}
  8.     queue := []*TreeNode{root}
  10.     for len(queue) > 0 {
  11.         n := len(queue)
  12.         level_tmp := []int{}
  14.         for i := 0; i < n; i++ {
  15.             root = queue[0]
  16.             queue = queue[1 :]
  18.             level_tmp = append(level_tmp, root.Val)
  19.             if root.Left != nil {
  20.                 queue = append(queue, root.Left) 
  21.             }
  22.             if root.Right != nil {
  23.                 queue = append(queue, root.Right)
  24.             }
  25.         }
  26.         levels = append(levels, level_tmp)        // + xxx 就倒序输出了
  27.     }
  28.     return levels
  29. }
//BFS    排成一排打印：[1, 2, 3]
func levelOrder(root *TreeNode) []int {
    if root == nil {
        return nil
    }

    levels := []int{}
    queue := []*TreeNode{root}

    for len(queue) > 0 {
        root = queue[0]
        queue = queue[1 :]

        if root.Left != nil {
            queue = append(queue, root.Left) 
        }
        if root.Right != nil {
            queue = append(queue, root.Right)
        }

        levels = append(levels, root.Val)
    }
    return levels
}