Merge K Sorted Lists Using Min Heap in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push the first element of each list into the min heap.

DSA C++

for (int i = 0; i < lists.size(); i++) {
    if (lists[i] != nullptr) {
        minHeap.[1](lists[i]);
    }
}

Drag options to blanks, or click blank then click option'

Aempty

Bpop

Ctop

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of push to add elements.

Using top which only accesses the smallest element without adding.

We use push() to add elements to the min heap.

2fill in blank

medium

Complete the code to get the smallest node from the min heap.

DSA C++

while (!minHeap.empty()) {
    ListNode* node = minHeap.[1]();
    minHeap.pop();
    // process node
}

Drag options to blanks, or click blank then click option'

Atop

Bpop

Cpush

Dempty

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() to get the element, which removes it immediately.

Using push() which adds elements instead of accessing.

top() returns the smallest element in the min heap without removing it.

3fill in blank

hard

Fix the error in the comparator struct for the min heap.

DSA C++

struct compare {
    bool operator() (ListNode* a, ListNode* b) {
        return a->val [1] b->val;
    }
};

Drag options to blanks, or click blank then click option'

A==

B>

C<

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' which creates a max heap instead of min heap.

Using '==' or '!=' which do not define order.

For a min heap, the comparator returns true if a's value is greater than b's value.

4fill in blank

hard

Fill both blanks to correctly add the next node to the min heap after popping the smallest node.

DSA C++

if (node->[1] != nullptr) {
    minHeap.[2](node->next);
}

Drag options to blanks, or click blank then click option'

Anext

Bprev

Cpush

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next' to access the next node.

Using pop instead of push to add the node.

We check if node->next exists and then push it into the min heap.

5fill in blank

hard

Fill all three blanks to correctly build the merged linked list.

DSA C++

ListNode dummy(0);
ListNode* tail = &dummy;

while (!minHeap.empty()) {
    ListNode* node = minHeap.[1]();
    minHeap.pop();
    tail->[2] = node;
    tail = tail->[3];

    if (node->next != nullptr) {
        minHeap.push(node->next);
    }
}

Drag options to blanks, or click blank then click option'

Atop

Bnext

Cval

Dprev

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() instead of top() to get the node.

Using 'val' or 'prev' instead of 'next' for linking.

We get the smallest node with top(), link it by setting tail->next, and move tail to tail->next.