Linear Search Algorithm in DSA Typescript - Build from Scratch

Linear Search Algorithm

📖 Scenario: You are helping a store manager find a specific product ID in the list of products available in the store.

🎯 Goal: Build a simple linear search algorithm to find the position of a product ID in an array of product IDs.

📋 What You'll Learn

Create an array called productIDs with exact values

Create a variable called targetID to hold the product ID to search

Use a for loop with variable i to search targetID in productIDs

Print the index of targetID if found, otherwise print -1

💡 Why This Matters

🌍 Real World

Stores and inventory systems often need to find if a product is available by checking product IDs one by one.

💼 Career

Understanding linear search helps in debugging and improving simple search tasks in software development and data handling.

1

Create the product ID list

Create an array called productIDs with these exact numbers: 101, 203, 405, 607, 809

DSA Typescript

// Your code here

Hint

Use square brackets [] to create an array and separate numbers with commas.

2

Set the target product ID

Create a variable called targetID and set it to 405

DSA Typescript

const productIDs = [101, 203, 405, 607, 809];
// Your code here

Hint

Use const to create a variable and assign the number 405.

3

Search for the target ID using linear search

Use a for loop with variable i to go through productIDs. Inside the loop, use an if statement to check if productIDs[i] equals targetID. If yes, print i and stop the loop.

DSA Typescript

const productIDs = [101, 203, 405, 607, 809];
const targetID = 405;
// Your code here

Hint

Use a for loop from 0 to productIDs.length. Use === to compare values. Use break to stop the loop when found.

4

Print -1 if target not found

Modify the code to print -1 if targetID is not found in productIDs. Use a variable called foundIndex initialized to -1. Update it inside the loop if found. After the loop, print foundIndex.

DSA Typescript

const productIDs = [101, 203, 405, 607, 809];
const targetID = 405;
// Your code here

Hint

Use a variable foundIndex set to -1 before the loop. Change it to i if found. Print it after the loop.

Practice

1. What is the main idea behind the Linear Search Algorithm?

easy

A. Divide the list into halves repeatedly to find the target

B. Check each element one by one until the target is found or list ends

C. Sort the list first then search using binary steps

D. Use a hash table to find the target instantly

Solution

1. Step 1: Understand linear search process

   Linear search checks each element in order, from start to end, to find the target.

2. Step 2: Compare with other search methods

   Binary search divides list, hash uses extra memory, but linear search is simple sequential check.

3. Final Answer:

   Check each element one by one until the target is found or list ends -> Option B

4. Quick Check:

   Linear search = sequential check [OK]

Hint: Linear search means checking items one by one [OK]

Common Mistakes:

• Confusing linear search with binary search
• Thinking linear search requires sorted list
• Assuming linear search is always fastest

2. Which of the following is the correct TypeScript syntax to start a linear search loop over an array arr?

easy

A. for (let i = 0; i < arr.length; i++)

B. for (let i = 1; i <= arr.length; i++)

C. for (let i = 0; i <= arr.length; i++)

D. for (let i = 1; i < arr.length; i++)

Solution

1. Step 1: Identify correct loop start and end

   Array indices start at 0 and go up to length-1, so loop must start at 0 and run while i < length.

2. Step 2: Check each option's loop condition

   for (let i = 0; i < arr.length; i++) uses i=0 and i < arr.length, which is correct. Others either start at 1 or use <= which causes out-of-bounds.

3. Final Answer:

   for (let i = 0; i < arr.length; i++) -> Option A

4. Quick Check:

   Loop from 0 to length-1 [OK]

Hint: Array loops start at 0 and run while less than length [OK]

Common Mistakes:

• Starting loop at 1 instead of 0
• Using <= instead of < causing index errors
• Confusing array length with last index

3. What will be the output of this TypeScript code?

const arr = [4, 7, 1, 9];
const target = 1;
let index = -1;
for (let i = 0; i < arr.length; i++) {
  if (arr[i] === target) {
    index = i;
    break;
  }
}
console.log(index);

medium

A. 1

B. -1

C. 2

D. 3

Solution

1. Step 1: Trace the loop and compare elements

   Check arr[0]=4 (not 1), arr[1]=7 (not 1), arr[2]=1 (match found), set index=2 and break loop.

2. Step 2: Output the index variable

   After loop, index is 2, so console.log prints 2.

3. Final Answer:

   2 -> Option C

4. Quick Check:

   Target found at index 2 [OK]

Hint: Stop at first match and print its index [OK]

Common Mistakes:

• Not breaking loop and returning last index
• Confusing index with value
• Assuming index starts at 1

4. Find the error in this linear search code snippet and choose the fix:

const arr = [5, 3, 8];
const target = 3;
let index = -1;
for (let i = 0; i <= arr.length; i++) {
  if (arr[i] === target) {
    index = i;
    break;
  }
}
console.log(index);

medium

A. Change loop condition to i < arr.length

B. Initialize index to 0 instead of -1

C. Remove the break statement

D. Change target to 5

Solution

1. Step 1: Identify loop boundary error

   The loop uses i <= arr.length, which causes i to reach arr.length, an invalid index (out of bounds).

2. Step 2: Fix loop condition to prevent out-of-bounds

   Changing condition to i < arr.length ensures i stays within valid indices 0 to length-1.

3. Final Answer:

   Change loop condition to i < arr.length -> Option A

4. Quick Check:

   Loop must run while i < length [OK]

Hint: Use < not <= for array index loops [OK]

Common Mistakes:

• Using <= causing runtime error
• Changing unrelated variables
• Removing break causing unnecessary iterations

5. You want to find the last occurrence of a target number in an array using linear search. Which modification to this code will achieve that?

const arr = [2, 5, 3, 5, 7];
const target = 5;
let index = -1;
for (let i = 0; i < arr.length; i++) {
  if (arr[i] === target) {
    index = i;
    break;
  }
}
console.log(index);

hard

A. Sort the array before searching

B. Add break after setting index to stop at first occurrence

C. Start loop from the end and break at first match

D. Remove the break statement to continue searching all elements

Solution

1. Step 1: Understand current code behavior

   The loop checks all elements; each time target matches, index updates to current i, so last match index remains after loop.

2. Step 2: Identify why removing break helps

   If break was present, loop would stop at first match. Removing break ensures full array is checked for last occurrence.

3. Final Answer:

   Remove the break statement to continue searching all elements -> Option D

4. Quick Check:

   Keep searching to find last occurrence [OK]

Hint: To find last occurrence, check all elements without break [OK]

Common Mistakes:

• Adding break stops search too early
• Sorting changes original order and index meaning
• Starting loop from end requires different logic