Question

the following code reads an input array, and constructs a BST from it. if the current arr[i] is a duplicate, of a node in the tree, then arr[i] is discarded. count in the struct node refers to the number of times a number appears in the array. fi refers to the first index of the element found in the array. after the insertion, i am doing a post-order traversal of the tree and printing the data, count and index (in this order). the output i am getting when i run this code is:

0 0 7
0 0 6

thank you for your help.

Jeev

 struct node{

    int data;
    struct node *left;
    struct node *right;
    int fi;
    int count;

};

struct node* binSearchTree(int arr[], int size);
int setdata(struct node**node, int data, int index);
void insert(int data, struct node **root, int index);
void sortOnCount(struct node* root);

void main(){

    int arr[] = {2,5,2,8,5,6,8,8};
    int size = sizeof(arr)/sizeof(arr[0]);
struct node* temp = binSearchTree(arr, size);
sortOnCount(temp);

}   

struct node* binSearchTree(int arr[], int size){

    struct node* root = (struct node*)malloc(sizeof(struct node));

    if(!setdata(&root, arr[0], 0))
        fprintf(stderr, "root couldn't be initialized");

    int i = 1;
    for(;i<size;i++){
        insert(arr[i], &root, i);
    }

    return root;
}    

int  setdata(struct node** nod, int data, int index){

    if(*nod!=NULL){

    (*nod)->fi = index;
    (*nod)->left = NULL;
    (*nod)->right = NULL;
    return 1;
}
return 0;
}

void insert(int data, struct node **root, int index){

struct node* new = (struct node*)malloc(sizeof(struct node));
setdata(&new, data, index);
struct node** temp = root;

while(1){

    if(data<=(*temp)->data){
        if((*temp)->left!=NULL)
            *temp=(*temp)->left;
        else{
            (*temp)->left = new;
            break;
        }
    }
    else if(data>(*temp)->data){
        if((*temp)->right!=NULL)
            *temp=(*temp)->right;
        else{
            (*temp)->right = new;
            break;
        }
    }
    else{
        (*temp)->count++;
        free(new);
        break;
    }
}



}

void sortOnCount(struct node* root){

if(root!=NULL){

    sortOnCount(root->left);
    sortOnCount(root->right);
    printf("%d %d %d\n", (root)->data, (root)->count, (root)->fi);
}   
}

Answer 1

Well, for one, you’re passing a pointer to a pointer in your insert function:

void insert(int data, struct node **root, int index);

And then you have a temporary variable:

struct node** temp = root;

that you use to traverse your tree. When you do that, you’re changing your root. Just pass a pointer, i.e.,

void insert(int data, node *root , int index){

Second, if(data<=(*temp)->data){ should JUST be <, not <=.

Hint: in general, it’s fairly rare when you actually need to pass a pointer to a pointer.