function heapSort(arr) {
    let n = arr.length;

    // Build max heap
    for (let i = Math.floor(n / 2) - 1; i >= 0; i--) {
        heapify(arr, n, i);
    }

    // Extract elements from heap one by one
    for (let i = n - 1; i > 0; i--) {
        // Move current root (largest) to end
        let temp = arr[0];
        arr[0] = arr[i];
        arr[i] = temp;

        // Call heapify on the reduced heap
        heapify(arr, i, 0);
    }
}

// Heapify a subtree rooted at index 'i'
// 'n' is the size of the heap
function heapify(arr, n, i) {
    let largest = i;  // Initialize largest as root
    let left = 2 * i + 1;  // Left child
    let right = 2 * i + 2; // Right child

    // If left child is larger than root
    if (left < n && arr[left] > arr[largest]) {
        largest = left;
    }

    // If right child is larger than largest so far
    if (right < n && arr[right] > arr[largest]) {
        largest = right;
    }

    // If largest is not root, swap and heapify
    if (largest !== i) {
        let swap = arr[i];
        arr[i] = arr[largest];
        arr[largest] = swap;

        // Recursively heapify the affected subtree
        heapify(arr, n, largest);
    }
}

// Test the heapSort function
let arr = [12, 11, 13, 5, 6, 7];
heapSort(arr);
console.log("Sorted array is:", arr);