Last Updated on May 12, 2023 by Prepbytes

Heapify is a common operation performed on binary heaps, which are data structures that are used to implement priority queues. It involves rearranging the elements in a heap to maintain the heap property, which ensures that the root element of the heap is always the highest (or lowest) priority element.

## Time Complexity of Heapify

The time complexity of the heapify operation is an important consideration when analyzing the performance of algorithms that use binary heaps. It determines the amount of time required to reorganize the heap after adding or removing elements and impacts the overall performance of the algorithm

The time complexity of heapify depends on the size of the heap and the depth of the heap, as well as the particular algorithm used to perform the operation. Several algorithms exist for heapify, including bottom-up heapify and top-down heapify, which have different time complexities and performance characteristics. Understanding these algorithms and their time complexities can help optimize the performance of algorithms that use binary heaps.

### Example of a Perfect Complete Binary Tree

The heart of heap data structure is the Heapify algorithm, which is used to maintain the second property of heap data structure i.e Heap order property. According to the heap order property in the min-heap, every node’s value must be smaller than its children and in the max-heap, every node’s value must be greater than its children.

**For example:**

### Time Complexity analysis of building a Heap

After every insertion, the Heapify algorithm is used to maintain the properties of the heap data structure. So, we will first discuss the time complexity of the Heapify algorithm.

**For example:**

### Pseudo Code

```
max_Heapify(A, i){
left_child = 2*i;
right_child = 2*i +1;
if(left_child <= A.heap_size() and A[left_child] > A[i])
largest = l;
else largest = i;
if(right_child <= A.heap_size() and A[right_child] > A[largest])
largest = r;
if(largest != i)
swap(A[largest],A[i])
max_Heapify(A,largest)
}
build_Max_Heap(A){
A.heap_size ← A.length
for i ← A.length/2 downto 1
max_Heapify(A, i)
}
```

From the above example, we can conclude that the Heapify algorithm’s time complexity is equal to O(height of the complete binary tree) i.e O(log N).

### Trivial Analysis:

Each call to MAX-HEAPIFY requires log(n) time, we make n such calls O(nlogn)

### Tighter Bound:

Each call to MAX-HEAPIFY requires time O(h) where h is the height of node i. Therefore running time is

**Conclusion**

In conclusion, the time complexity of the heapify operation is an important factor to consider when analyzing the performance of algorithms that use binary heaps. It determines the amount of time required to reorganize the heap after adding or removing elements and can impact the overall efficiency of the algorithm.

The time complexity of Heapify depends on the size of the heap and the depth of the heap, as well as the algorithm used to perform the operation. Bottom-up heapify and top-down heapify are two common algorithms used for heapify, each with different time complexities and performance characteristics.

It is important to understand the time complexity of heapify and choose the appropriate algorithm based on the size and depth of the heap, as well as the specific requirements of the algorithm being implemented. By optimizing the heapify operation, the overall performance of algorithms that use binary heaps can be improved.

## Frequently Asked Questions

**Q1. What is the worst-case time complexity of heapify?**

**Ans.** The worst-case time complexity of heapify depends on the algorithm used. The worst-case time complexity of bottom-up heapify is O(n), where n is the size of the heap. The worst-case time complexity of top-down heapify is O(n log n), where n is the size of the heap.

**Q2. Is the time complexity of heapify affected by the depth of the heap?**

**Ans.** Yes, the time complexity of heapify is affected by the depth of the heap. The deeper the heap, the longer it takes to perform the heapify operation. This is because heapify involves swapping elements in the heap, and the number of swaps required increases as the depth of the heap increases.

**Q3. What is the difference between bottom-up heapify and top-down heapify?**

**Ans.** Bottom-up heapify starts at the lowest level of the heap and works its way up to the root, while top-down heapify starts at the root and works its way down to the lowest level of the heap. Bottom-up heapify has a time complexity of O(n), while top-down heapify has a time complexity of O(log n). Bottom-up heapify is typically faster for large heaps, while top-down heapify is faster for small heaps.

**Q4. Can the time complexity of heapify be improved?**

**Ans.** The time complexity of heapify is determined by the algorithm used, but there are ways to optimize the operation. For example, using a binary heap with a Fibonacci heap can reduce the worst-case time complexity of heapify to O(log n), making it more efficient than traditional binary heaps.

**Q5. Is heapify always necessary when working with binary heaps?**

**Ans.** Heapify is necessary when working with binary heaps to maintain the heap property and ensure that the highest (or lowest) priority element is always at the root of the heap. Without heapify, the performance of algorithms that use binary heaps would be severely impacted.