grid47 Exploring patterns and algorithms
Sep 23, 2024
9 min read
Solution to LeetCode 449: Serialize and Deserialize BST Problem
Design an algorithm to serialize and deserialize a binary search tree (BST). Serialization is converting the tree to a string format, while deserialization reconstructs the tree from this string. The goal is to ensure that the BST can be serialized to a compact string and can be accurately deserialized back into the original tree structure.
Problem
Approach
Steps
Complexity
Input: The input consists of the root node of a binary search tree, where each node contains an integer value, a left child, and a right child.
Example: [3,1,4,null,2]
Constraints:
• The number of nodes in the tree is in the range [0, 10^4].
• 0 <= Node.val <= 10^4.
• The tree is a valid binary search tree (BST).
Output: The output is a string representing the serialized binary search tree. The serialized string should be as compact as possible while ensuring it can be deserialized back into the original tree.
Example: [3,1,4,null,2]
Constraints:
• The serialized string should accurately represent the structure of the binary search tree.
Goal: The goal is to implement efficient serialization and deserialization methods for a binary search tree.
Steps:
• 1. For serialization, traverse the tree and convert each node's value into a string format, ensuring that the null nodes are also represented.
• 2. For deserialization, read the serialized string, and rebuild the tree structure by placing nodes in the correct positions based on the BST properties.
Goal: The input consists of a binary search tree with integer values, and the serialized string must compactly represent the tree.
Steps:
• The number of nodes in the tree is between 0 and 10^4.
• Node values are between 0 and 10^4.
• The tree is guaranteed to be a valid binary search tree.
Assumptions:
• The input tree is a valid binary search tree.
• The serialized string should be compact and able to be deserialized back into the original tree.
• Input: [3,1,4,null,2]
• Explanation: In this case, the tree is represented as a string where 'null' is used to indicate the absence of a node.
• Input: []
• Explanation: An empty tree is represented by an empty string.
Approach: We will implement two functions: one for serialization and one for deserialization. The serialization function will traverse the tree and convert it into a string. The deserialization function will reconstruct the tree from the string, ensuring that the BST structure is preserved.
Observations:
• Serialization involves converting the tree to a string in a way that preserves its structure.
• Deserialization requires careful parsing of the serialized string to recreate the tree with the correct structure.
• To serialize, we can use a pre-order traversal and represent the tree in a compact string format. For deserialization, we will parse the string and build the tree using the BST properties.
Steps:
• 1. Implement a function to serialize the tree. This will involve performing a pre-order traversal of the tree, converting each node's value to a string, and appending it to the result string.
• 2. Implement a function to deserialize the tree. This will involve parsing the serialized string and constructing the tree by following the BST property (i.e., values to the left are smaller, values to the right are larger).
Empty Inputs:
• Handle the case where the input tree is empty.
Large Inputs:
• The algorithm should be able to handle up to 10^4 nodes efficiently.
Special Values:
• Ensure the tree can handle special values such as zero or the maximum possible value (10^4).
Constraints:
• The algorithm must work within the time and space constraints specified.
*structTreeNode {
*int val;
* TreeNode *left;
* TreeNode *right;
*TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/classCodec {
public:// Encodes a tree to a single string.
string serialize(TreeNode* root) {
string str;
serial(str, root);
return str;
}
voidserial(string& ss, TreeNode* root) {
if (!root) return;
char c[4];
memcpy(c, &(root->val), sizeof(int));
for (int i =0; i <4; i++) ss.push_back(c[i]);
serial(ss, root->left );
serial(ss, root->right);
}
// Decodes your encoded data to tree.
TreeNode*deserialize(string data) {
int pos =0;
return deserial(data, pos, INT_MIN, INT_MAX);
}
TreeNode*deserial(string& data, int& pos, int left, int right) {
if (pos >= data.size()) returnNULL;
int val;
memcpy(&val, &(data[pos]), sizeof(int));
if (val < left || val > right) returnNULL;
TreeNode* root =new TreeNode(val);
pos +=sizeof(int);
root->left = deserial ( data, pos, left, val );
root->right = deserial ( data, pos, val, right );
return root;
}
};
// Your Codec object will be instantiated and called as such:
// Codec* ser = new Codec();
// Codec* deser = new Codec();
// string tree = ser->serialize(root);
// TreeNode* ans = deser->deserialize(tree);
1 : Structure Definition
*structTreeNode {
Defines a struct `TreeNode` representing a node in the binary tree, with an integer value and pointers to its left and right children.
2 : Structure Fields
*int val;
The `val` field stores the integer value of the node.
3 : Structure Fields
* TreeNode *left;
The `left` pointer points to the left child of the node.
4 : Structure Fields
* TreeNode *right;
The `right` pointer points to the right child of the node.
