Serialize and Deserialize BST
<p>Serialization is converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be reconstructed later in the same or another computer environment.</p>

<p>Design an algorithm to serialize and deserialize a <b>binary search tree</b>. There is no restriction on how your serialization/deserialization algorithm should work. You need to ensure that a binary search tree can be serialized to a string, and this string can be deserialized to the original tree structure.</p>

<p><b>The encoded string should be as compact as possible.</b></p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> root = [2,1,3]
<strong>Output:</strong> [2,1,3]
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> root = []
<strong>Output:</strong> []
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the tree is in the range <code>[0, 10<sup>4</sup>]</code>.</li>
	<li><code>0 &lt;= Node.val &lt;= 10<sup>4</sup></code></li>
	<li>The input tree is <strong>guaranteed</strong> to be a binary search tree.</li>
</ul>
Tree; Depth-First Search; Breadth-First Search; Design; Binary Search Tree; String; Binary Tree
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */

type Codec struct {
}

func Constructor() Codec {
	return Codec{}
}

// Serializes a tree to a single string.
func (this *Codec) serialize(root *TreeNode) string {
	if root == nil {
		return ""
	}
	data := &strings.Builder{}
	var dfs func(*TreeNode)
	dfs = func(root *TreeNode) {
		if root == nil {
			return
		}
		data.WriteString(strconv.Itoa(root.Val))
		data.WriteByte(' ')
		dfs(root.Left)
		dfs(root.Right)
	}
	dfs(root)
	return data.String()[0 : data.Len()-1]
}

// Deserializes your encoded data to tree.
func (this *Codec) deserialize(data string) *TreeNode {
	if data == "" {
		return nil
	}
	vals := strings.Split(data, " ")
	i := 0
	var dfs func(int, int) *TreeNode
	dfs = func(mi, mx int) *TreeNode {
		if i == len(vals) {
			return nil
		}
		x, _ := strconv.Atoi(vals[i])
		if x < mi || x > mx {
			return nil
		}
		i++
		root := &TreeNode{Val: x}
		root.Left = dfs(mi, x)
		root.Right = dfs(x, mx)
		return root
	}
	return dfs(math.MinInt64, math.MaxInt64)
}

/**
 * Your Codec object will be instantiated and called as such:
 * ser := Constructor()
 * deser := Constructor()
 * tree := ser.serialize(root)
 * ans := deser.deserialize(tree)
 * return ans
 */