算法1

(按照前序遍历来序列化与反序列化二叉树) $O(n^2)$

C++ 代码

//参考yxc
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    string serialize(TreeNode* root) {
        string res;
        //if (!root) return res;
        dfs_s(root, res);
        return res;
    }   
    void dfs_s(TreeNode* root, string & res) {
        if (!root) {
            res += "null ";//这个是null加空格。。。。
            return;
        }
        res += to_string(root->val) + ' ';
        dfs_s(root->left, res);
        dfs_s(root->right, res);
    }
    TreeNode* deserialize(string data) {
        int u = 0;
        return dfs_d(data, u);
    }
    TreeNode * dfs_d(string data, int &u) {
        if(u == data.size()) return NULL;
        int k = u ;
        while(data[k] != ' ') k++;
        if (data[u] == 'n') {
            u = k + 1;
            return NULL;
        }
        int sum = 0;
        for (int i = u; i < k; i ++) {
            sum = sum * 10 + data[i] - '0';
        }
        u = k + 1;
        auto root = new TreeNode(sum);
        root->left = dfs_d(data, u);
        root->right = dfs_d(data, u);
        return root;
    }
};