You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: Solution.go
    path of file: ./repos/awesome-golang-algorithm/leetcode/101-200/0104.Maximum-Depth-of-Binary-Tree
    
    the code of the file until where you have to start completion: package Solution

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

func maxDepth_1(root *TreeNode) int {
	if r
    
func maxDepth_3(root *TreeNode) int {
	ans, que := 0, make([]*TreeNode, 0)
	if root == nil {
		return 0
	}
	que = append(que, root)
	for len(que) > 0 {
		length := len(que)
		for i := 0; i < length; i++ {
			node := que[0]
			que = que[1:]
			if node.Left != nil {
				que = append(que, node.Left)
			}
			if node.Right != nil {
				que = append(que, node.Right)
			}
		}
		ans++
	}
	return ans
}