Kth Smallest Element Using Min Heap in DSA Javascript - Build from Scratch

Kth Smallest Element Using Min Heap

📖 Scenario: You are working with a list of numbers representing daily temperatures. You want to find the kth smallest temperature to understand cooler days.

🎯 Goal: Build a program that uses a min heap to find the kth smallest number in a list.

📋 What You'll Learn

Create an array called temperatures with exact values

Create a variable k to select the kth smallest element

Build a min heap from the temperatures array

Extract the kth smallest element from the min heap

Print the kth smallest temperature

💡 Why This Matters

🌍 Real World

Finding the kth smallest or largest value is useful in statistics, data analysis, and real-time systems like temperature monitoring or stock prices.

💼 Career

Understanding heaps and kth element selection is important for software engineers working on algorithms, data processing, and performance optimization.

1

Create the temperatures array

Create an array called temperatures with these exact values: [23, 17, 35, 12, 28, 30, 15]

DSA Javascript

# Create the temperatures array
// Your code here

Hint

Use const temperatures = [23, 17, 35, 12, 28, 30, 15]; to create the array.

2

Set the kth position

Create a variable called k and set it to 3 to find the 3rd smallest temperature

DSA Javascript

const temperatures = [23, 17, 35, 12, 28, 30, 15];
// Set k to 3
// Your code here

Hint

Use const k = 3; to set the kth smallest element to find.

3

Build min heap and extract kth smallest

Create a min heap from temperatures using a MinHeap class, then extract the smallest element k times to find the kth smallest temperature

DSA Javascript

const temperatures = [23, 17, 35, 12, 28, 30, 15];
const k = 3;

// Implement MinHeap class and find kth smallest
// Your code here

Hint

Build a MinHeap class with insert and extractMin methods. Insert all temperatures, then extract min k times.

4

Print the kth smallest temperature

Print the variable kthSmallest to display the kth smallest temperature

DSA Javascript

const temperatures = [23, 17, 35, 12, 28, 30, 15];
const k = 3;

class MinHeap {
  constructor() {
    this.heap = [];
  }

  getParentIndex(i) { return Math.floor((i - 1) / 2); }
  getLeftChildIndex(i) { return 2 * i + 1; }
  getRightChildIndex(i) { return 2 * i + 2; }

  swap(i, j) {
    [this.heap[i], this.heap[j]] = [this.heap[j], this.heap[i]];
  }

  insert(value) {
    this.heap.push(value);
    this.heapifyUp();
  }

  heapifyUp() {
    let index = this.heap.length - 1;
    while (index > 0) {
      let parentIndex = this.getParentIndex(index);
      if (this.heap[parentIndex] > this.heap[index]) {
        this.swap(parentIndex, index);
        index = parentIndex;
      } else {
        break;
      }
    }
  }

  extractMin() {
    if (this.heap.length === 0) return null;
    if (this.heap.length === 1) return this.heap.pop();

    const min = this.heap[0];
    this.heap[0] = this.heap.pop();
    this.heapifyDown();
    return min;
  }

  heapifyDown() {
    let index = 0;
    const length = this.heap.length;
    while (this.getLeftChildIndex(index)  this.heap[smallerChildIndex]) {
        this.swap(index, smallerChildIndex);
        index = smallerChildIndex;
      } else {
        break;
      }
    }
  }
}

const minHeap = new MinHeap();
for (const temp of temperatures) {
  minHeap.insert(temp);
}

let kthSmallest = null;
for (let i = 0; i < k; i++) {
  kthSmallest = minHeap.extractMin();
}

// Print the kth smallest temperature
console.log(kthSmallest);

Hint

Use console.log(kthSmallest); to print the result.