Top K Frequent Elements Using Heap in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a map that counts frequencies of elements.

DSA C++

std::unordered_map<int, int> freqMap;
for (int num : nums) {
    freqMap[num] [1];
}

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

A--

B++

C=

D*=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' instead of '++' resets the count instead of increasing it.

Using '--' decreases the count which is incorrect here.

We use ++ to increase the count of each number in the frequency map.

2fill in blank

medium

Complete the code to push pairs of (frequency, number) into the priority queue.

DSA C++

std::priority_queue<std::pair<int, int>> maxHeap;
for (auto& p : freqMap) {
    maxHeap.[1](std::make_pair(p.second, p.first));
}

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

Apush

Bpop

Ctop

Dempty

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop instead of push removes elements instead of adding.

Using top or empty does not add elements.

We use push to add elements into the priority queue.

3fill in blank

hard

Fix the error in the loop that extracts top k elements from the heap.

DSA C++

std::vector<int> result;
for (int i = 0; i < k; i++) {
    result.push_back(maxHeap.[1]().second);
    maxHeap.pop();
}

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

Atop

Bpop

Cpush

Dempty

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() to access element causes error because pop() returns void.

Using push() or empty() are incorrect for accessing elements.

We use top() to access the element at the top of the heap before popping it.

4fill in blank

hard

Fill both blanks to create a min-heap that stores pairs of (frequency, number).

DSA C++

auto cmp = [](const std::pair<int, int>& a, const std::pair<int, int>& b) {
    return a.[1] > b.[2];
};
std::priority_queue<std::pair<int, int>, std::vector<std::pair<int, int>>, decltype(cmp)> minHeap(cmp);

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Afirst

Bsecond

Csize

Dempty

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing 'second' compares the number, not frequency.

Using size or empty are invalid for pair elements.

We compare the 'first' element of pairs which is frequency to create a min-heap.

5fill in blank

hard

Fill all three blanks to insert elements into the min-heap and maintain size k.

DSA C++

for (auto& p : freqMap) {
    minHeap.[1](p);
    if (minHeap.[2]() > k) {
        minHeap.[3]();
    }
}

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

Apush

Bsize

Cpop

Dtop

Attempts:

3 left

💡 Hint

Common Mistakes

Using top() instead of size() to check heap size.

Using pop() before checking size causes errors.

We push elements, check size, and pop smallest to keep top k frequent elements.