Searching in a BST

Procedure :

• Start from the root node.

• Compare the data in each node with the key. If it matches, return pointer to that node.

• If the key is lesser than the data in the node, move pointer to the left child.

• If the key is greater than the data in the node, move pointer to the right child.

• If pointer becomes null, it means the we have reached the end of the tree and the element was not found. Therefore, return NULL.

Iterative Function :

struct Node *BSTsearch(struct Node *ptr, int key) {

    while (ptr != NULL) {
        if (key == ptr -> data) {
            return ptr;
        } else if (key < ptr -> data) {
            ptr = ptr -> left;
        } else {
            ptr = ptr -> right;
        }
    }
    return NULL;
    
}

Recursive Function :

struct Node *BSTsearch(struct Node *ptr, int key) {

    if (ptr == NULL) {
        return NULL;
    }
    
    if (key == ptr -> data) {
        return ptr;
    } else if (key < ptr -> data) {
        return BSTsearch(ptr -> left, key);
    } else {
        return BSTsearch(ptr -> right, key);
    }

}

Time Complexity : O(log n)

Contributed by Nitin Ranganath