剑指 32 - III. Z字形打印二叉树 👌

剑指 Offer 32 - III. 从上到下打印二叉树 III

和力扣 103. 二叉树的锯齿形层序遍历一致

//2，bfs常规解
func levelOrder(root *TreeNode) [][]int {
    if root == nil {
        return nil
    }
    levels := [][]int{}
    queue := []*TreeNode{root}
    for len(queue) > 0 {
        n := len(queue)
        level_tmp := []int{}
        for i := 0; i < n; i++ {
            root = queue[0]
            queue = queue[1 :]
            level_tmp = append(level_tmp, root.Val)
            if root.Left != nil {
                queue = append(queue, root.Left) 
            }
            if root.Right != nil {
                queue = append(queue, root.Right)
            }
        }
        k := len(level_tmp)
        if len(levels) % 2 == 1  {              //说明levels是层数【】外数组，level是内数组【】
            for i := 0; i < k / 2; i++ {
                level_tmp[i], level_tmp[k - 1 - i] = level_tmp[k - 1 - i], level_tmp[i]
            }
        }
        levels = append(levels, level_tmp)
    }
    return levels
}