Heap Patterns

Master Heap Patterns for DSA + Competitive Programming

A Heap provides O(log n) insert/delete with O(1) access to the smallest (min-heap) or largest (max-heap) element.

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Pattern Table

Pattern	Typical Questions	Trigger
Priority Queue Basics	Min/max tracking	Heap of size K
Top K Elements	Kth largest, top frequent	Min-heap of size K
Kth Smallest/Largest	Kth element	Heap + size control
Merge K Sorted	Merge K lists	Min-heap of heads
Median / Two Heaps	Running median	Max-heap + Min-heap
Heap Sort	Sort using heap	Build heap + extract

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Mental Trigger

Smallest/largest K → Top K → Min-heap of size K.

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Generic Java Heap Template (Base)

PriorityQueue<Integer> minHeap = new PriorityQueue<>();
PriorityQueue<Integer> maxHeap = new PriorityQueue<>(Collections.reverseOrder());

minHeap.offer(val);     // insert
minHeap.peek();         // smallest
minHeap.poll();         // remove smallest

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Recognition Cheat Sheet

If you see…	Think…
Kth largest/smallest	Heap of size K
Top K frequent	Freq map + min-heap
Merge K sorted lists	Min-heap of heads
Running median	Two heaps