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mediumDSA

What is a heap / priority queue?

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01

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Explain heaps.

heappriority-queue
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A heap is a complete binary tree maintaining the heap property (min-heap: parent ≤ children). It gives O(1) peek of min/max and O(log n) insert/extract — backing priority queues. Useful for top-k problems, Dijkstra's algorithm, and scheduling.

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04

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k largest with a heap
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import heapq

def k_largest(nums, k):
    heap = []                      # min-heap of size k
    for n in nums:
        heapq.heappush(heap, n)
        if len(heap) > k:
            heapq.heappop(heap)    # drop the smallest
    return sorted(heap, reverse=True)


# --- demo --- (or the built-in: heapq.nlargest(k, nums))
print(k_largest([3, 1, 5, 12, 2, 11], 3))   # [12, 11, 5]
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