golang力扣leetcode 107. 二叉树的层序遍历 II

107. 二叉树的层序遍历 II

107. 二叉树的层序遍历 II

题解

就是上一篇博文加一个翻转

代码

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
}