题目描述

blablabla

样例

blablabla

算法1

/**
 * 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;
        dfs_s(root,res);
        return res;
    }

    void dfs_s(TreeNode* root, string &res) {
        if (!root) {
            res+="null ";
            return;
        }
        res+=to_string(root->val)+' ';
        dfs_s(root->left, res);
        dfs_s(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;
        bool f=false;
        if (data[u]=='-') u++,f=!f;
        for (int i=u;i<k;i++) val=val*10+(data[i]-'0');
        if (f) val*=-1;
        auto root=new TreeNode(val);
        u=k+1;
        root->left=dfs_d(data,u);
        root->right=dfs_d(data,u);
        return root;
    }
};