build heap algorithm

// Function to build a Max-Heap from the given array 
void buildHeap(int arr[], int n) 
{ 
    // Index of last non-leaf node 
    int startIdx = (n / 2) - 1; 
  
    // Perform reverse level order traversal 
    // from last non-leaf node and heapify 
    // each node 
    for (int i = startIdx; i >= 0; i--) { 
        heapify(arr, n, i); 
    } 
}