Heap Sort
📘 Data Structure and Algorithm
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📅 Nov 05, 2025
⏱ Estimated reading time: 1 min
Heap Sort Algorithm
Heap Sort is a comparison-based sorting algorithm that uses a binary heap data structure to efficiently find and remove the largest (or smallest) element repeatedly.
Algorithm Steps
- Build a max heap from the input data.
- Swap the root (maximum) with the last element.
- Reduce the heap size and heapify again.
- Repeat until all elements are sorted.
Example (C++)
void heapify(int arr[], int n, int i) {
int largest = i;
int l = 2 * i + 1;
int r = 2 * i + 2;
if (l < n && arr[l] > arr[largest])
largest = l;
if (r < n && arr[r] > arr[largest])
largest = r;
if (largest != i) {
swap(arr[i], arr[largest]);
heapify(arr, n, largest);
}
}
void heapSort(int arr[], int n) {
for (int i = n / 2 - 1; i >= 0; i--)
heapify(arr, n, i);
for (int i = n - 1; i > 0; i--) {
swap(arr[0], arr[i]);
heapify(arr, i, 0);
}
}
Time Complexity
- All Cases: O(n log n)
Advantages
- Consistent O(n log n) performance.
- In-place sorting, no extra space needed.
Disadvantages
- Not a stable sort.
- More complex than insertion or selection sort.
Conclusion
Heap Sort is a reliable, efficient, and in-place sorting algorithm widely used where consistent performance is required.
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