Description
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.
Design an algorithm to serialize and deserialize a binary search tree. 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.
The encoded string should be as compact as possible.
Example 1:
Input: root = [2,1,3]
Output: [2,1,3]
Example 2:
Input: root = []
Output: []
Constraints:
- The number of nodes in the tree is in the range
[0, 104].
0 <= Node.val <= 104- The input tree is guaranteed to be a binary search tree.
Solutions
Solution 1
PythonJavaC++Go
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Codec:
def serialize(self, root: Optional[TreeNode]) -> str:
"""Encodes a tree to a single string."""
def dfs(root: Optional[TreeNode]):
if root is None:
return
nums.append(root.val)
dfs(root.left)
dfs(root.right)
nums = []
dfs(root)
return " ".join(map(str, nums))
def deserialize(self, data: str) -> Optional[TreeNode]:
"""Decodes your encoded data to tree."""
def dfs(mi: int, mx: int) -> Optional[TreeNode]:
nonlocal i
if i == len(nums) or not mi <= nums[i] <= mx:
return None
x = nums[i]
root = TreeNode(x)
i += 1
root.left = dfs(mi, x)
root.right = dfs(x, mx)
return root
nums = list(map(int, data.split()))
i = 0
return dfs(-inf, inf)
# Your Codec object will be instantiated and called as such:
# Your Codec object will be instantiated and called as such:
# ser = Codec()
# deser = Codec()
# tree = ser.serialize(root)
# ans = deser.deserialize(tree)
# return ans(code-box)
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Codec {
private int i;
private List<String> nums;
private final int inf = 1 << 30;
// Encodes a tree to a single string.
public String serialize(TreeNode root) {
nums = new ArrayList<>();
dfs(root);
return String.join(" ", nums);
}
// Decodes your encoded data to tree.
public TreeNode deserialize(String data) {
if (data == null || "".equals(data)) {
return null;
}
i = 0;
nums = Arrays.asList(data.split(" "));
return dfs(-inf, inf);
}
private void dfs(TreeNode root) {
if (root == null) {
return;
}
nums.add(String.valueOf(root.val));
dfs(root.left);
dfs(root.right);
}
private TreeNode dfs(int mi, int mx) {
if (i == nums.size()) {
return null;
}
int x = Integer.parseInt(nums.get(i));
if (x < mi || x > mx) {
return null;
}
TreeNode root = new TreeNode(x);
++i;
root.left = dfs(mi, x);
root.right = dfs(x, mx);
return root;
}
}
// Your Codec object will be instantiated and called as such:
// Codec ser = new Codec();
// Codec deser = new Codec();
// String tree = ser.serialize(root);
// TreeNode ans = deser.deserialize(tree);
// return ans;(code-box)
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Codec {
public:
// Encodes a tree to a single string.
string serialize(TreeNode* root) {
if (!root) {
return "";
}
string data = "";
function<void(TreeNode*)> dfs = [&](TreeNode* root) {
if (!root) {
return;
}
data += to_string(root->val) + " ";
dfs(root->left);
dfs(root->right);
};
dfs(root);
data.pop_back();
return data;
}
// Decodes your encoded data to tree.
TreeNode* deserialize(string data) {
if (data.empty()) {
return nullptr;
}
vector<int> nums = split(data, ' ');
int i = 0;
function<TreeNode*(int, int)> dfs = [&](int mi, int mx) -> TreeNode* {
if (i == nums.size() || nums[i] < mi || nums[i] > mx) {
return nullptr;
}
int x = nums[i++];
TreeNode* root = new TreeNode(x);
root->left = dfs(mi, x);
root->right = dfs(x, mx);
return root;
};
return dfs(INT_MIN, INT_MAX);
}
vector<int> split(const string& s, char delim) {
vector<int> tokens;
stringstream ss(s);
string token;
while (getline(ss, token, delim)) {
tokens.push_back(stoi(token));
}
return tokens;
}
};
// Your Codec object will be instantiated and called as such:
// Codec* ser = new Codec();
// Codec* deser = new Codec();
// string tree = ser->serialize(root);
// TreeNode* ans = deser->deserialize(tree);
// return ans;(code-box)
/**
* 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
*/(code-box)
