297. Serialize and Deserialize Binary Tree

Description

Serialization is the process of 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 tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure.

Clarification: The input/output format is the same as how LeetCode serializes a binary tree. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself.

Example 1:

Input: root = [1,2,3,null,null,4,5]
Output: [1,2,3,null,null,4,5]

Example 2:

Input: root = []
Output: []

Constraints:

The number of nodes in the tree is in the range [0, 10⁴].
-1000 <= Node.val <= 1000

Solutions

Solution 1

Python Code

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# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None


class Codec:
    def serialize(self, root):
        """Encodes a tree to a single string.

        :type root: TreeNode
        :rtype: str
        """

        if root is None:
            return ''
        res = []

        def preorder(root):
            if root is None:
                res.append("#,")
                return
            res.append(str(root.val) + ",")
            preorder(root.left)
            preorder(root.right)

        preorder(root)
        return ''.join(res)

    def deserialize(self, data):
        """Decodes your encoded data to tree.

        :type data: str
        :rtype: TreeNode
        """
        if not data:
            return None
        vals = data.split(',')

        def inner():
            first = vals.pop(0)
            if first == '#':
                return None
            return TreeNode(int(first), inner(), inner())

        return inner()


# Your Codec object will be instantiated and called as such:
# ser = Codec()
# deser = Codec()
# ans = deser.deserialize(ser.serialize(root))

Java Code

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Codec {
    private static final String NULL = "#";
    private static final String SEP = ",";

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

    private void preorder(TreeNode root, StringBuilder sb) {
        if (root == null) {
            sb.append(NULL + SEP);
            return;
        }
        sb.append(root.val + SEP);
        preorder(root.left, sb);
        preorder(root.right, sb);
    }

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        if (data == null || "".equals(data)) {
            return null;
        }
        List<String> vals = new LinkedList<>();
        for (String x : data.split(SEP)) {
            vals.add(x);
        }
        return deserialize(vals);
    }

    private TreeNode deserialize(List<String> vals) {
        String first = vals.remove(0);
        if (NULL.equals(first)) {
            return null;
        }
        TreeNode root = new TreeNode(Integer.parseInt(first));
        root.left = deserialize(vals);
        root.right = deserialize(vals);
        return root;
    }
}

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

C++ Code

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/**
 * 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 s = "";
        preorder(root, s);
        return s;
    }

    void preorder(TreeNode* root, string& s) {
        if (!root)
            s += "# ";
        else {
            s += to_string(root->val) + " ";
            preorder(root->left, s);
            preorder(root->right, s);
        }
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        if (data == "") return nullptr;
        stringstream ss(data);
        return deserialize(ss);
    }

    TreeNode* deserialize(stringstream& ss) {
        string first;
        ss >> first;
        if (first == "#") return nullptr;
        TreeNode* root = new TreeNode(stoi(first));
        root->left = deserialize(ss);
        root->right = deserialize(ss);
        return root;
    }
};

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

TypeScript Code

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/**
 * 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 {
    return JSON.stringify(root);
}

/*
 * Decodes your encoded data to tree.
 */
function deserialize(data: string): TreeNode | null {
    return JSON.parse(data);
}

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

Rust Code

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// Definition for a binary tree node.
// #[derive(Debug, PartialEq, Eq)]
// pub struct TreeNode {
//   pub val: i32,
//   pub left: Option<Rc<RefCell<TreeNode>>>,
//   pub right: Option<Rc<RefCell<TreeNode>>>,
// }
//
// impl TreeNode {
//   #[inline]
//   pub fn new(val: i32) -> Self {
//     TreeNode {
//       val,
//       left: None,
//       right: None
//     }
//   }
// }
use std::rc::Rc;
use std::cell::RefCell;
struct Codec {}

/**
 * `&self` means the method takes an immutable reference.
 * If you need a mutable reference, change it to `&mut self` instead.
 */
impl Codec {
    fn new() -> Self {
        Codec {}
    }

    fn serialize(&self, root: Option<Rc<RefCell<TreeNode>>>) -> String {
        if root.is_none() {
            return String::from("#");
        }
        let mut node = root.as_ref().unwrap().borrow_mut();
        let left = node.left.take();
        let right = node.right.take();
        format!("{},{},{}", self.serialize(right), self.serialize(left), node.val)
    }

    fn deserialize(&self, data: String) -> Option<Rc<RefCell<TreeNode>>> {
        if data.len() == 1 {
            return None;
        }
        Self::renew(&mut data.split(",").collect())
    }

    fn renew(vals: &mut Vec<&str>) -> Option<Rc<RefCell<TreeNode>>> {
        let val = vals.pop().unwrap_or("#");
        if val == "#" {
            return None;
        }
        Some(
            Rc::new(
                RefCell::new(TreeNode {
                    val: val.parse().unwrap(),
                    left: Self::renew(vals),
                    right: Self::renew(vals),
                })
            )
        )
    }
}/**
 * Your Codec object will be instantiated and called as such:
 * let obj = Codec::new();
 * let data: String = obj.serialize(strs);
 * let ans: Option<Rc<RefCell<TreeNode>>> = obj.deserialize(data);
 */

JavaScript Code

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/**
 * 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) {
    return rserialize(root, '');
};

/**
 * Decodes your encoded data to tree.
 *
 * @param {string} data
 * @return {TreeNode}
 */
var deserialize = function (data) {
    const dataArray = data.split(',');
    return rdeserialize(dataArray);
};

const rserialize = (root, str) => {
    if (root === null) {
        str += '#,';
    } else {
        str += root.val + '' + ',';
        str = rserialize(root.left, str);
        str = rserialize(root.right, str);
    }
    return str;
};

const rdeserialize = dataList => {
    if (dataList[0] === '#') {
        dataList.shift();
        return null;
    }

    const root = new TreeNode(parseInt(dataList[0]));
    dataList.shift();
    root.left = rdeserialize(dataList);
    root.right = rdeserialize(dataList);

    return root;
};

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

Solution 2

TypeScript Code

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/**
 * 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 == null) {
        return '#';
    }
    const { val, left, right } = root;
    return `${val},${serialize(left)},${serialize(right)}`;
}

/*
 * Decodes your encoded data to tree.
 */
function deserialize(data: string): TreeNode | null {
    const n = data.length;
    if (n === 1) {
        return null;
    }
    const vals = data.split(',').reverse();
    const renew = () => {
        const val = vals.pop();
        if (val == null || val === '#') {
            return null;
        }
        return new TreeNode(Number(val), renew(), renew());
    };
    return renew();
}

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

297. Serialize and Deserialize Binary Tree#

Description#

Solutions#

Solution 1#

Solution 2#

297. Serialize and Deserialize Binary Tree

Description

Solutions

Solution 1

Solution 2