Question

297. Serialize and Deserialize Binary Tree

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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

# 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))

/**
 * 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));

/**
 * 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));

/**
 * 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));
 */

// 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);
 */

/**
 * 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

/**
 * 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));
 */