Serialize And Deserialize Bst

                                            
// Your solution code for Serialize and Deserialize BST goes here

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Codec {
public:

    // Encodes a tree to a single string.
    string serialize(TreeNode* root) {
        if (root == nullptr) return "null";

        string s = to_string(root->val) + " ";
        s += serialize(root->left) + " ";
        s += serialize(root->right);

        return s;
    }

    // Decodes your encoded data to tree.
    TreeNode* deserializeUtil(queue<string>& nodes) {
        if (nodes.empty() || nodes.front() == "null") {
            nodes.pop();
            return nullptr;
        }

        TreeNode* root = new TreeNode(stoi(nodes.front()));
        nodes.pop();
        root->left = deserializeUtil(nodes);
        root->right = deserializeUtil(nodes);

        return root;
    }

    TreeNode* deserialize(string data) {
        istringstream ss(data);
        queue<string> nodes;
        string str;

        while (ss >> str) {
            nodes.push(str);
        }

        return deserializeUtil(nodes);
    }
};

// Your Codec object will be instantiated and called as such:
// Codec ser, deser;
// TreeNode* ans = deser.deserialize(ser.serialize(root));

                                            
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int val) { this.val = val; }
 * }
 */

public class Codec {
    
    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {
        if (root == null) return "";
        StringBuilder sb = new StringBuilder();
        serializeHelper(root, sb);
        return sb.toString();
    }

    private void serializeHelper(TreeNode node, StringBuilder sb) {
        if (node == null) return;
        sb.append(node.val).append(",");
        serializeHelper(node.left, sb);
        serializeHelper(node.right, sb);
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        if (data.isEmpty()) return null;
        String[] values = data.split(",");
        Queue<Integer> queue = new LinkedList<>();
        for (String val : values) {
            queue.offer(Integer.parseInt(val));
        }
        return deserializeHelper(queue, Integer.MIN_VALUE, Integer.MAX_VALUE);
    }

    private TreeNode deserializeHelper(Queue<Integer> queue, int lower, int upper) {
        if (queue.isEmpty()) return null;
        int val = queue.peek();
        if (val < lower || val > upper) return null;
        queue.poll();
        TreeNode node = new TreeNode(val);
        node.left = deserializeHelper(queue, lower, val);
        node.right = deserializeHelper(queue, val, upper);
        return node;
    }
}

                                            
# 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):
        def _serialize(node):
            if not node:
                return 'None'
            return str(node.val) + ',' + _serialize(node.left) + ',' + _serialize(node.right)
        
        return _serialize(root)
    
    def deserialize(self, data):
        def _deserialize(nodes):
            if nodes[0] == 'None':
                nodes.popleft()
                return None
            root = TreeNode(int(nodes[0]))
            nodes.popleft()
            root.left = _deserialize(nodes)
            root.right = _deserialize(nodes)
            return root
        
        data = collections.deque(data.split(','))
        return _deserialize(data)

                                            
/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */

/**
 * Encodes a tree to a single string.
 *
 * @param {TreeNode} root
 * @return {string}
 */
var serialize = function(root) {
    if (!root) return '';
    
    let result = [];
    
    function dfs(node) {
        if (node) {
            result.push(node.val);
            dfs(node.left);
            dfs(node.right);
        } else {
            result.push('#');
        }
    }
    
    dfs(root);
    
    return result.join(',');
};

/**
 * Decodes your encoded data to tree.
 *
 * @param {string} data
 * @return {TreeNode}
 */
var deserialize = function(data) {
    if (!data) return null;
    
    data = data.split(',');
    
    function buildTree() {
        if (data.length === 0) return null;
        
        let val = data.shift();
        if (val === '#') {
            return null;
        }
        
        let node = new TreeNode(parseInt(val));
        node.left = buildTree();
        node.right = buildTree();
        
        return node;
    }
    
    return buildTree();
};

/**
 * Your functions will be called as such:
 * deserialize(serialize(root));
 */

                                            
/**
* Definition for a binary tree node.
* class TreeNode {
*     val: number
*     left: TreeNode | null
*     right: TreeNode | null
*     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
*         this.val = (val===undefined ? 0 : val)
*         this.left = (left===undefined ? null : left)
*         this.right = (right===undefined ? null : right)
*     }
* }
*
* Encodes a tree to a single string.
*/
function serialize(root: TreeNode | null): string {
    if (!root) return '';
    
    const queue = [root];
    const result: string[] = [];
    
    while (queue.length > 0) {
        const node = queue.shift();
        if (node) {
            result.push(node.val.toString());
            queue.push(node.left, node.right);
        } else {
            result.push('null');
        }
    }
    
    return result.join(',');
};

/**
* Decodes your encoded data to tree.
*/
function deserialize(data: string): TreeNode | null {
    if (!data) return null;
    
    const values = data.split(',');
    const root = new TreeNode(parseInt(values[0]));
    const queue = [root];
    let i = 1;
    
    while (queue.length > 0) {
        const node = queue.shift();
        if (values[i] !== 'null') {
            const left = new TreeNode(parseInt(values[i]));
            node.left = left;
            queue.push(left);
        }
        i++;
        if (values[i] !== 'null') {
            const right = new TreeNode(parseInt(values[i]));
            node.right = right;
            queue.push(right);
        }
        i++;
    }
    
    return root;
};

                                            
import java.util.LinkedList

/**
 * Definition for a binary tree node.
 * class TreeNode(var `val`: Int) {
 *     var left: TreeNode? = null
 *     var right: TreeNode? = null
 * }
 */

class Codec() {

    // Encodes a tree to a single string.
    fun serialize(root: TreeNode?): String {
        val sb = StringBuilder()
        serializeHelper(root, sb)
        return sb.toString()
    }

    private fun serializeHelper(node: TreeNode?, sb: StringBuilder) {
        if (node == null) {
            sb.append("null,")
            return
        }
        sb.append(node.`val`).append(",")
        serializeHelper(node.left, sb)
        serializeHelper(node.right, sb)
    }

    // Decodes your encoded data to tree.
    fun deserialize(data: String): TreeNode? {
        val nodes = LinkedList<String>()
        nodes.addAll(data.split(","))
        return deserializeHelper(nodes)
    }

    private fun deserializeHelper(nodes: LinkedList<String>): TreeNode? {
        if (nodes.isEmpty() || nodes.first() == "null") {
            nodes.removeFirst()
            return null
        }

        val rootValue = nodes.removeFirst().toInt()
        val root = TreeNode(rootValue)
        root.left = deserializeHelper(nodes)
        root.right = deserializeHelper(nodes)
        return root
    }
}

                                            
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */

type Codec struct {
}

func (this *Codec) serialize(root *TreeNode) string {
    if root == nil {
        return ""
    }
    return strconv.Itoa(root.Val) + "," + this.serialize(root.Left) + "," + this.serialize(root.Right)
}

func (this *Codec) deserialize(data string) *TreeNode {
    nums := strings.Split(data, ",")
    var buildTree func() *TreeNode
    buildTree = func() *TreeNode {
        if nums[0] == "" {
            nums = nums[1:]
            return nil
        }
        val, _ := strconv.Atoi(nums[0])
        root := &TreeNode{Val: val}
        nums = nums[1:]
        root.Left = buildTree()
        root.Right = buildTree()
        return root
    }
    return buildTree()
}

func Constructor() Codec {
    return Codec{}
}

To solve this coding challenge, we need to develop two methods: one to serialize a Binary Search Tree (BST) to a string and another to deserialize that string back to the original BST. Serialization involves converting the tree structure into a string format that can be easily stored or transmitted, while deserialization involves reconstructing the tree from this string representation.

Explanation

Steps to Serialize

Define the Node Structure :

We need a structure to represent our tree nodes.

Recursive Tree Traversal :

We'll use a recursive method to traverse through the tree and convert it into a string. The method will handle
None

(empty) nodes, appending a special marker (e.g., 'None') for such cases, ensuring we maintain the tree structure.

Concatenate Values :

As we traverse, we'll concatenate the node values in a pre-order traversal manner (node value, then left subtree, then right subtree) with a separator (e.g., comma).

Steps to Deserialize

Split String to List :

Convert the serialized string back into a list of node values using the same separator.

Recursive Tree Reconstruction :

Implement a recursive method to convert the list back into the tree. If a 'None' marker is encountered, it corresponds to an empty node. For other values, create tree nodes and recursively assign their left and right children.

Detailed Steps in Pseudocode

Serialization

Define TreeNode Class :

This should contain properties for value, left child, and right child.

Serialize Function :

Call a helper recursive function
_serialize(node)

starting with the root node.

_serialize(node) Function:

If
node

is
None

, return the marker 'None'.
Otherwise, return the string of the current node's value, plus the result of
_serialize(node.left)

, plus the result of
_serialize(node.right)

, concatenated with commas.

Deserialization

Deserialize Function :

Split the input string into a list of node values.
Call a helper recursive function
_deserialize(nodes_list)

starting with this list.

_deserialize(nodes_list) Function:

If the first element is 'None', remove it from the list and return
None

.
Create a new TreeNode with the integer value of the first element, remove it from the list.
Set this node's left child by recursively calling
_deserialize(nodes_list)

.
Set this node's right child by recursively calling
_deserialize(nodes_list)

again.
Return the constructed node.

Pseudocode

                                            
# TreeNode class definition
class TreeNode:
    def __init__(value):
        self.value = value
        self.left = None
        self.right = None

# Serializer class definition
class Codec:

    # Serialize function
    def serialize(root):
        # Helper function to perform pre-order traversal
        def _serialize(node):
            if node is None:
                return 'None'
            # Serialize current node value + left subtree + right subtree
            return str(node.value) + ',' + _serialize(node.left) + ',' + _serialize(node.right)
        
        # Initiate serialization from root
        return _serialize(root)

    # Deserialize function
    def deserialize(data):
        # Convert string to list of values
        node_values = data.split(',')

        # Helper function to reconstruct the tree
        def _deserialize(nodes_list):
            if nodes_list[0] == 'None':
                nodes_list.pop(0) # Remove 'None' marker
                return None
            
            # Create node with the current value
            node = TreeNode(int(nodes_list.pop(0)))
            
            # Construct left and right subtrees
            node.left = _deserialize(nodes_list)
            node.right = _deserialize(nodes_list)
            
            return node
        
        # Initiate deserialization with list of node values
        return _deserialize(node_values)

In conclusion, the pseudocode provides a method for both converting a binary search tree into a string representation and reconstructing it back from that string. The key steps involve recursive tree traversal, careful handling of

None

markers, and splitting/rebuilding from a list of values. This comprehensive approach ensures that the structure and values of the original tree are perfectly conserved through serialization and deserialization.