LC_00297_SerializeAndDeserializeBinaryTree.cpp

/*
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.
For example, you may serialize the following tree
    1
   / \
  2   3
     / \
    4   5

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

Credits:
Special thanks to @Louis1992 for adding this problem and creating all test cases.

Hide Tags Tree Design
*/

/**
 * 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;
        stack<TreeNode*> stk;
        stk.push(root);
        while (stk.size()) {
            TreeNode* node = stk.top();
            stk.pop();
            if (node) {
                out << node->val << ' ';
                stk.push(node->right);
                stk.push(node->left);
            } else {
                out << "# ";
            }
        }
        return out.str();
    }

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

private:
    TreeNode* deserializeHelper(istringstream& in) {
        string val;
        in >> val;
        if (val == "#")
            return NULL;
        TreeNode* root = new TreeNode(stoi(val));
        root->left = deserializeHelper(in);
        root->right = deserializeHelper(in);
        return root;
    }
};

class Codec {
public:
    // Encodes a tree to a single string.
    string serialize(TreeNode* root) {
        ostringstream out;
        serializeHelper(root, out);
        return out.str();
    }

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

private:
    void serializeHelper(TreeNode* root, ostringstream& out) {
        if (root) {
            out << root->val << ' ';
            serializeHelper(root->left, out);
            serializeHelper(root->right, out);
        } else {
            out << "# ";
        }
    }

    TreeNode* deserializeHelper(istringstream& in) {
        string val;
        in >> val;
        if (val == "#")
            return NULL;
        TreeNode* root = new TreeNode(stoi(val));
        root->left = deserializeHelper(in);
        root->right = deserializeHelper(in);
        return root;
    }
};

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