solution.go

package leetcode

/*
 * @lc app=leetcode.cn id=107 lang=golang
 *
 * [107] 二叉树的层次遍历 II
 */

// @lc code=start
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */

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

func levelOrderBottom(root *TreeNode) [][]int {
	var res [][]int
	if root == nil {
		return res
	}
	queue := []*TreeNode{root}

	for len(queue) > 0 {
		l := len(queue)
		list := make([]int, 0)
		for i := 0; i < l; i++ {
			node := queue[i]
			list = append(list, node.Val)
			if node.Left != nil {
				queue = append(queue, node.Left)
			}
			if node.Right != nil {
				queue = append(queue, node.Right)
			}
		}
		res = append([][]int{list}, res...)
		queue = queue[l:]
	}
	return res
}

// @lc code=end