[LeetCode] Serialize and Deserialize Binary Tree

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.

Example: 

You may serialize the following tree:

    1
   / \
  2   3
     / \
    4   5

as "[1,2,3,null,null,4,5]"

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

Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.

序列化和反序列化二叉树。

使用输入和输出字符串流istringstream、ostringstream。

序列化：从根结点开始，如果结点存在，将值存入输出字符串流。然后对其左右子节点递归调用序列化函数。

反序列化：先读入第一个字符，以生成一个根结点。然后对根结点的左右子节点去序列化。

/**
 * 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) {
        ostringstream out;
        serialize(root, out);
        return out.str();
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        istringstream in(data);
        return deserialize(in);
    }

private:
    void serialize(TreeNode* root, ostringstream& out)
    {
        if (root)
        {
            out << root->val << " ";
            serialize(root->left, out);
            serialize(root->right, out);
        }
        else
        {
            out << "# ";
        }
    }
    TreeNode* deserialize(istringstream& in)
    {
        string val;
        in >> val;
        if (val == "#")
            return NULL;
        TreeNode* root = new TreeNode(stoi(val));
        root->left = deserialize(in);
        root->right = deserialize(in);
        return root;
    }
};

// Your Codec object will be instantiated and called as such:
// Codec codec;
// codec.deserialize(codec.serialize(root));

利用queue进行迭代。

/**
 * 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 "";
        ostringstream out;
        queue<TreeNode*> q;
        q.push(root);
        while (!q.empty())
        {
            TreeNode* node = q.front();
            q.pop();
            if (node)
            {
                out << node->val << " ";
                q.push(node->left);
                q.push(node->right);
            }
            else
            {
                out << "# ";
            }
        }
        return out.str();
    }

    // Decodes your encoded data to tree.
    TreeNode* deserialize(string data) {
        if (data.empty())
            return NULL;
        istringstream in(data);
        queue<TreeNode*> q;
        string val;
        in >> val;
        TreeNode* root = new TreeNode(stoi(val));
        TreeNode* cur = root;
        q.push(cur);
        while (!q.empty())
        {
            TreeNode* node = q.front();
            q.pop();
            if (!(in >> val))
                break;
            if (val != "#")
            {
                cur = new TreeNode(stoi(val));
                q.push(cur);
                node->left = cur;
            }
            if (!(in >> val))
                break;
            if (val != "#")
            {
                cur = new TreeNode(stoi(val));
                q.push(cur);
                node->right = cur;
            }
        }
        return root;
    }
};

// Your Codec object will be instantiated and called as such:
// Codec codec;
// codec.deserialize(codec.serialize(root));