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Insert in Binary Search Tree

+4 votes
asked Oct 19, 2022 by Aki Ha (160 points)

When I print the entire tree it prints the values 30 and 50, but I have recently changed it to have two pointers: Node *a, *b; a = insertNode(NULL, 1) b = insertNode(a, 2) However the b pointer just points to the root node - I believe this is an issue in the insertNode function in what I return. I want to return the newly added leaf node not the original root node, but I am unsure of how to do this.

    typedef struct _Node{
        int data;
        struct _Node *left, *right;
    Node *insertNode(Node *root, int value){
        if(root == NULL){
            Node *temp = (Node*)malloc(sizeof(Node));
            temp->data = value;
            temp->left = temp->right = NULL;
            return temp;
        if(root->data < value){
            root->right = insertNode(root->right, value);
        else if(root->data > value){
            root->left = insertNode(root->left, value);
        return root;
void printNode( Node * pnode )
   if( pnode )
       printf( "node at %p : left=%p, right=%p, data=%d\n",
           pnode, pnode->left, pnode->right, pnode->data );
       if( pnode->left )
           printNode( pnode->left );
       if( pnode->right )
           printNode( pnode->right );
       printf( "node is null\n" );
    int main(){
        Node *a;
        a = insertNode(NULL, 30);
        a = insertNode(a, 50);
        b = insertNode(a, 70);        
        b = insertNode(a, 80);
        b = insertNode(a, 90);
//I only want to print out 70,80,90 rather than the whole tree 30,50,70,80,90

1 Answer

0 votes
answered Oct 20, 2022 by Peter Minarik (88,130 points)
edited Oct 20, 2022 by Peter Minarik

I think what you need is this:

    if (root->data < value)
        return root->right = insertNode(root->right, value);
    else if(root->data > value)
        return root->left = insertNode(root->left, value);

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