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 search tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary search tree can be serialized to a string and this string can be deserialized to the original tree structure.
The encoded string should be as compact as possible.
Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.
这道题让我们对二叉搜索树序列化和去序列化，跟之前那道Serialize and Deserialize Binary Tree极其相似，虽然题目中说编码成的字符串要尽可能的紧凑，但是我们并没有发现跟之前那题有何不同，而且也没有看到能够利用BST性质的方法，姑且就按照之前题目的解法来写吧：
解法一：
class Codec {
public:
// Encodes a tree to a single string.
string serialize(TreeNode* root) {
ostringstream os;
serialize(root, os);
return os.str();
}
// Decodes your encoded data to tree.
TreeNode* deserialize(string data) {
istringstream is(data);
return deserialize(is);
}
void serialize(TreeNode* root, ostringstream& os) {
if (!root) os << "# ";
else {
os << root->val << " ";
serialize(root->left, os);
serialize(root->right, os);
}
}
TreeNode* deserialize(istringstream& is) {
string val = "";
is >> val;
if (val == "#") return NULL;
TreeNode* node = new TreeNode(stoi(val));
node->left = deserialize(is);
node->right = deserialize(is);
return node;
}
};
另一种方法是层序遍历的非递归解法，这种方法略微复杂一些，我们需要借助queue来做，本质是BFS算法，也不是很难理解，就是BFS算法的常规套路稍作修改即可，参见代码如下：
解法二：
class Codec {
public:
// Encodes a tree to a single string.
string serialize(TreeNode* root) {
if (!root) return "";
ostringstream os;
queue<TreeNode*> q;
q.push(root);
while (!q.empty()) {
TreeNode *t = q.front(); q.pop();
if (t) {
os << t->val << " ";
q.push(t->left);
q.push(t->right);
} else {
os << "# ";
}
}
return os.str();
}
// Decodes your encoded data to tree.
TreeNode* deserialize(string data) {
if (data.empty()) return NULL;
istringstream is(data);
queue<TreeNode*> q;
string val = "";
is >> val;
TreeNode *res = new TreeNode(stoi(val)), *cur = res;
q.push(cur);
while (!q.empty()) {
TreeNode *t = q.front(); q.pop();
if (!(is >> val)) break;
if (val != "#") {
cur = new TreeNode(stoi(val));
q.push(cur);
t->left = cur;
}
if (!(is >> val)) break;
if (val != "#") {
cur = new TreeNode(stoi(val));
q.push(cur);
t->right = cur;
}
}
return res;
}
};
类似题目：
Serialize and Deserialize Binary Tree
Find Duplicate Subtrees
Serialize and Deserialize N-ary Tree
参考资料：
https://leetcode.com/problems/serialize-and-deserialize-bst
https://leetcode.com/problems/serialize-and-deserialize-bst/discuss/93260/easy-bfs-java
LeetCode All in One 题目讲解汇总(持续更新中...)
