针对测试用例有负数的新的题解

blablabla

样例

/**
 * 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:

    // Encodes a tree to a single string.
    string serialize(TreeNode* root) {
        string res;
        Pre(root, res);
        return res;


    }
    void Pre(TreeNode* root, string &res)
    {
        if(!root)
        {
            res += "null ";
            return;
        }
        res += to_string(root->val) + ' ';
        Pre(root->left, res);
        Pre(root->right, res);
    }

    // Decodes your encoded data to tree.
    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 val = 0;
        for(int i = u; i < k; i++)
        {
            if(data[i] == '-')
            {
                i++;
                val = val * 10 + data[i] - '0';
            }
            else
            {
                val = val * 10 + data[i] - '0';
            }

        }
        if(data[u] == '-')
        {
            val = 0 - val;
        }
         u = k + 1;
        auto  root = new TreeNode(val);
        root->left = dfs_d(data, u);
        root->right = dfs_d(data, u);

        return root;
    }
};

算法1

(暴力枚举) $O(n^2)$

blablabla

时间复杂度分析：blablabla

C++ 代码

blablabla

算法2

(暴力枚举) $O(n^2)$

blablabla

时间复杂度分析：blablabla

C++ 代码

blablabla