606. Construct String from Binary Tree

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 
11 static int wing=[]()
12 {
13     std::ios::sync_with_stdio(false);
14     cin.tie(NULL);
15     return 0;
16 }();
17 
18 class Solution 
19 {
20 public:
21     string tree2str(TreeNode* t) 
22     {
23         return travel(t);
24     }
25     
26     string travel(TreeNode* root)
27     {
28         if(root==NULL)
29             return "";
30         if(root->left==NULL&&root->right==NULL)
31             return to_string(root->val);
32         else if(root->right==NULL)
33             return to_string(root->val)+"("+travel(root->left)+")";
34         else
35             return to_string(root->val)+"("+travel(root->left)+")"+"("+travel(root->right)+")";
36     }
37 };

递归，问题不大，还挺好理解的