题目：序列化二叉树
请实现两个函数，分别用来序列化和反序列化二叉树。
示例:
你可以将以下二叉树：
1
/ \
2 3
/ \
4 5
序列化为 "[1,2,3,null,null,4,5]"
解题：
/*** 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 {
private:// 1,2,#,#,3,-4,#,#,5,#,#,void encode(TreeNode* root, string& res) {if (!root) {res += "#,";return;}res += to_string(root->val) + ",";encode(root->left, res);encode(root->right, res);}TreeNode* decode(int& p, const string& data) {if (data[p] == '#') {p += 2;return NULL;}bool isN = false;if (data[p] == '-') { // 负数的情况isN = true;p++;}int num = 0; // 还原成整数while (data[p] != ',') {num = num * 10 + data[p] - '0';p++;}p++;if (isN) num = -num;auto root = new TreeNode(num);root->left = decode(p, data);root->right = decode(p, data);return root;}public:// Encodes a tree to a single string.string serialize(TreeNode* root) {string res = "";encode(root, res);return res;}// Decodes your encoded data to tree.TreeNode* deserialize(string data) {int p = 0;return decode(p, data);}
};