BST to DLL Code failing

#1 
void help(Node* root, Node* &head){
    if(!root)   return;
    
    Node *left = root->left, *right = root->right;
    help(left,head);
    
    if(!pre){
        pre = root;
        head = root;
    }else{
        root->left = pre;
        pre->right = root;
    }
    root->right = head;
    head->left = root;
    pre = root;
    help(right,head);
    return;
}

Node *bTreeToCList(Node *root)
{
    if(!root)   return root;
    Node* head = NULL;
    help(root,head);
    return head;
}

This code is failing on some test cases. Please explain y.

#2

hey @Hyperian are you failing 3,4 & 5 test case number?

#3

Try Submitting this code

void help(Node* root, Node* &head){
    if(root == NULL)   return;
    
    Node *left = root->left, *right = root->right;
    help(left,head);
    
    if(!pre){
       // pre = root;
        head = root;
    }else{
        root->left = pre;
        pre->right = root;
    }
    /*root->right = head;
    head->left = root;
    */
    pre = root;
    help(right,head);
}

Node *bTreeToCList(Node *root)
{
    if(root == NULL)   return NULL;
    Node* head = NULL;
    help(root,head);
    return head;
}
#4

this was for simple bst to dll, ya commented out line were for circular dll. I trieed this code over gfg but failed there, dont know why. Showing error on submission case even though the case passes it run in a custom input.

#5

Share the link where you are submitting this code.

#6

https://practice.geeksforgeeks.org/problems/binary-tree-to-dll/1

#7

Your logic was correct just some issue with the implementation which i have resolved here

Node* help(Node* root, Node* &pre){
    if(root == NULL)   return root;
    Node* head = help(root->left, pre);
    
    if(!pre){
       // pre = root;
        head = root;
    }else{
        pre->right = root;
        root->left = pre;
    }
    /*root->right = head;
    head->left = root;
    */
    pre = root;
    help(root->right,pre);
    return head;
}

Node * bToDLL(Node *root)
{
    // your code here
     if(root == NULL)   return NULL;
    Node* head = NULL;
    return help(root,head);
}

It’s getting accepted as you can see here

image
image1366×768 94.8 KB

#8

I cannot understand the issue with my code.

#9

There were only 2 sections of your code which were causing error In accepting your code and they were

And

Also the return statement in which I have returned the head
Rest it’s same

#10

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