给定一个二叉树的dfs遍历结果(NULL记为*)，重构二叉树，返回头节点

 1 #include <bits/stdc++.h> 
 2 using namespace std; 
 3 
 4 struct TreeNode{
 5     char val;
 6     TreeNode* left;
 7     TreeNode* right;
 8     TreeNode(char nval){
 9         val = nval;
10         left = NULL;
11         right = NULL;
12     }    
13 }; 
14 
15 TreeNode* construct(string str){
16     if(str.empty()) return NULL;
17     
18     stack<TreeNode*> temp;
19     TreeNode* root = new TreeNode(str[0]);    
20     temp.push(root);
21     
22     for(int i=1; i<str.size(); i++){
23         if( str[i]>=‘a‘ && str[i]<=‘z‘ ){
24             TreeNode* newNode = new TreeNode(str[i]);
25             while(temp.top()->left && temp.top()->right ) temp.pop();
26             
27             if(temp.top()->left ==NULL) temp.top()->left = newNode;
28             else if(temp.top()->right==NULL ) {
29                 temp.top()->right= newNode;
30             }            
31             temp.push(newNode);                        
32         }    
33         else if(str[i]==‘*‘){
34             TreeNode* newNode = new TreeNode(str[i]);
35             if(temp.top()->left ==NULL) temp.top()->left = newNode;
36             else if( temp.top()->right==NULL ){
37                 temp.top()->right = newNode;
38                 temp.pop();
39             } 
40         }
41         
42     } 
43     
44     //按层遍历,将*改为NULL   
45     queue<TreeNode*> que;
46     TreeNode* cur = NULL;
47     que.push(root);    
48     while( !que.empty() ){
49         int size = que.size();
50         while(size--){
51             cur = que.front();
52             que.pop();
53             if(cur->left && cur->left->val==‘*‘){
54                 cur->left = NULL;
55             }    
56             if(cur->left && cur->left->val!=‘*‘){
57                 que.push(cur->left);
58             }
59             
60             if(cur->right && cur->right->val == ‘*‘){
61                 cur->right = NULL;
62             }
63             if(cur->right && cur->right->val !=‘*‘){
64                 que.push(cur->right);
65             }            
66         }         
67     }
68         
69     return root;
70     
71 } 
72 
73 void search(TreeNode* root, string& res){
74     if(root==NULL){
75         res+=‘*‘;
76         return;
77     } 
78 //    res += root->val;
79     search(root->left, res);    
80     res += root->val;
81     search(root->right, res);
82 }
83 
84 
85 int main(){
86 //    string str = "abdm***n**ew**cf**g**";
87     string str = "ab*gf***c*de**f**"; 
88     TreeNode* root = construct(str);
89         
90     string out="";
91     search(root, out);
92     
93     cout<<out<<endl;
94     
95 }