Build Heap from Array Heapify in DSA Javascript - Build from Scratch

Build Heap from Array Heapify

📖 Scenario: Imagine you have a list of numbers representing tasks with different priorities. You want to organize them so the highest priority task is always easy to find. This is like arranging a pile of books so the biggest book is always on top.

🎯 Goal: You will build a max heap from an unsorted array using the heapify process. This means rearranging the array so each parent number is bigger than its children, making it easy to get the largest number quickly.

📋 What You'll Learn

Create an array called tasks with the exact numbers: [4, 10, 3, 5, 1]

Create a variable called n that stores the length of the tasks array

Write a function called heapify that takes tasks, n, and i as parameters and rearranges the array to maintain max heap property

Use a for loop to call heapify starting from the last parent node down to the root

Print the tasks array after building the max heap

💡 Why This Matters

🌍 Real World

Heaps are used in task scheduling, priority queues, and sorting algorithms like heapsort.

💼 Career

Understanding heap data structures helps in software engineering roles involving efficient data processing and algorithm optimization.

1

Create the initial array

Create an array called tasks with these exact numbers: [4, 10, 3, 5, 1]

DSA Javascript

// Create the array tasks with the numbers [4, 10, 3, 5, 1]
// Your code here

Hint

Use const tasks = [4, 10, 3, 5, 1]; to create the array.

2

Set the length variable

Create a variable called n that stores the length of the tasks array

DSA Javascript

const tasks = [4, 10, 3, 5, 1];
// Create a variable n that stores the length of tasks
// Your code here

Hint

Use const n = tasks.length; to get the array length.

3

Write the heapify function

Write a function called heapify that takes tasks, n, and i as parameters and rearranges the array to maintain max heap property. Use variables largest, left, and right inside the function.

DSA Javascript

const tasks = [4, 10, 3, 5, 1];
const n = tasks.length;
// Write the heapify function below
// Your code here

Hint

Use the heapify logic to compare parent and children and swap if needed, then call heapify recursively.

4

Build the heap and print the result

Use a for loop starting from Math.floor(n / 2) - 1 down to 0 to call heapify(tasks, n, i). Then print the tasks array using console.log(tasks).

DSA Javascript

const tasks = [4, 10, 3, 5, 1];
const n = tasks.length;

function heapify(tasks, n, i) {
    let largest = i;
    let left = 2 * i + 1;
    let right = 2 * i + 2;

    if (left  tasks[largest]) {
        largest = left;
    }

    if (right  tasks[largest]) {
        largest = right;
    }

    if (largest !== i) {
        let temp = tasks[i];
        tasks[i] = tasks[largest];
        tasks[largest] = temp;

        heapify(tasks, n, largest);
    }
}

// Use a for loop to build the heap and then print tasks
// Your code here

Hint

Start from the last parent node and call heapify down to the root. Then print the array.