Insert at Middle Specific Position in DSA Typescript - Build from Scratch

Insert at Middle Specific Position

📖 Scenario: You are managing a queue of people waiting for a ride at an amusement park. Sometimes, a new person arrives and wants to join the queue at a specific position in the middle, not just at the front or the end.

🎯 Goal: Build a program that inserts a new person into a queue (represented as an array) at a specific middle position.

📋 What You'll Learn

Create an array called queue with exact names of people waiting

Create a variable called newPerson with the exact name to insert

Create a variable called position with the exact index where the new person should be inserted

Insert newPerson into queue at position

Print the updated queue showing the order of people

💡 Why This Matters

🌍 Real World

Queues are common in real life, like waiting lines or task scheduling. Sometimes people or tasks need to be added in the middle, not just at the end.

💼 Career

Understanding how to insert elements at specific positions in arrays or lists is important for managing ordered data in software development, such as event handling, UI lists, or scheduling.

1

Create the initial queue

Create an array called queue with these exact names in order: 'Alice', 'Bob', 'Charlie', 'David', 'Eva'

DSA Typescript

// Create the queue array with the given names
// Your code here

Hint

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

2

Set the new person and position

Create a variable called newPerson and set it to 'Frank'. Create a variable called position and set it to 2.

DSA Typescript

const queue = ['Alice', 'Bob', 'Charlie', 'David', 'Eva'];
// Create newPerson and position variables
// Your code here

Hint

Use const to create variables and assign the exact values.

3

Insert the new person at the specific position

Use the splice method on queue to insert newPerson at index position without removing any elements.

DSA Typescript

const queue = ['Alice', 'Bob', 'Charlie', 'David', 'Eva'];
const newPerson = 'Frank';
const position = 2;
// Insert newPerson into queue at position
// Your code here

Hint

The splice method can insert elements by specifying the start index, number of elements to remove (0 here), and the new element.

4

Print the updated queue

Print the queue array to show the order of people after insertion.

DSA Typescript

const queue = ['Alice', 'Bob', 'Charlie', 'David', 'Eva'];
const newPerson = 'Frank';
const position = 2;
queue.splice(position, 0, newPerson);
// Print the queue array
// Your code here

Hint

Use console.log(queue) to print the array.

Practice

1. What does inserting at a specific middle position in a linked list mean?

easy

A. Adding a new node only at the beginning of the list

B. Removing a node from the middle of the list

C. Adding a new node only at the end of the list

D. Adding a new node exactly at the given position counting from the start

Solution

1. Step 1: Understand insertion position

   Inserting at a specific middle position means placing the new node exactly at that position counting from the start of the list.

2. Step 2: Differentiate from other insertions

   Insertion at beginning or end is different; here we insert inside the list at a given index.

3. Final Answer:

   Adding a new node exactly at the given position counting from the start -> Option D

4. Quick Check:

   Insert at position = Add node at that index [OK]

Hint: Insert means add node exactly at given index [OK]

Common Mistakes:

• Confusing insertion with deletion
• Thinking insertion only happens at start or end
• Ignoring the position index

2. Which of the following TypeScript code snippets correctly inserts a node with value 10 at position 2 in a singly linked list?

easy

A. function insertAtPosition(head, val, pos) { let newNode = {value: val, next: null}; let current = head; for(let i=1; i

B. function insertAtPosition(head, val, pos) { let newNode = {value: val, next: null}; let current = head; for(let i=0; i

C. function insertAtPosition(head, val, pos) { let newNode = {value: val, next: null}; newNode.next = head; head = newNode; return head; }

D. function insertAtPosition(head, val, pos) { let newNode = {value: val, next: null}; head.next = newNode; return head; }

Solution

1. Step 1: Analyze loop for position

   The loop runs from 1 to pos-2 to reach node before insertion point (pos-1).

2. Step 2: Insert new node correctly

   New node's next points to current.next, then current.next updated to new node.

3. Final Answer:

   Code in option A correctly inserts at position 2 -> Option A

4. Quick Check:

   Loop to pos-1, link new node [OK]

Hint: Loop to node before position, then insert [OK]

Common Mistakes:

• Looping too far or too short
• Not updating newNode.next correctly
• Inserting at wrong position index

3. What will be the linked list after inserting value 99 at position 3 in the list 1 -> 2 -> 3 -> 4 -> null using the following TypeScript code?

function insertAtPosition(head, val, pos) {
  let newNode = {value: val, next: null};
  if (pos === 1) {
    newNode.next = head;
    return newNode;
  }
  let current = head;
  for (let i = 1; i < pos - 1; i++) {
    current = current.next;
  }
  newNode.next = current.next;
  current.next = newNode;
  return head;
}

// Initial list: 1 -> 2 -> 3 -> 4 -> null
// Insert 99 at position 3
let head = {value:1, next:{value:2, next:{value:3, next:{value:4, next:null}}}};
head = insertAtPosition(head, 99, 3);

medium

A. 1 -> 2 -> 3 -> 4 -> 99 -> null

B. 1 -> 2 -> 99 -> 3 -> 4 -> null

C. 99 -> 1 -> 2 -> 3 -> 4 -> null

D. 1 -> 99 -> 2 -> 3 -> 4 -> null

Solution

1. Step 1: Traverse to node before position 3

   Loop runs i=1 to pos-2=1, so current moves to node with value 2.

2. Step 2: Insert new node after current

   New node 99 points to current.next (node 3), current.next updated to new node.

3. Final Answer:

   1 -> 2 -> 99 -> 3 -> 4 -> null -> Option B

4. Quick Check:

   Insert at pos 3 places 99 after 2 [OK]

Hint: Insert after node at pos-1 [OK]

Common Mistakes:

• Inserting at wrong position
• Not updating links correctly
• Confusing position indexing

4. Identify the error in the following TypeScript function that tries to insert a node at position 2 in a linked list.

function insertAtPosition(head, val, pos) {
  let newNode = {value: val, next: null};
  let current = head;
  for(let i = 0; i < pos - 1; i++) {
    current = current.next;
  }
  newNode.next = current.next;
  current.next = newNode;
  return head;
}

medium

A. The loop runs one step too many, causing current to be null before insertion

B. The newNode.next is not assigned correctly

C. The function does not handle insertion at position 1

D. The function returns newNode instead of head

Solution

1. Step 1: Analyze loop range

   The loop runs from i=0 to pos-2, moving current pos-1 times, which moves current too far.

2. Step 2: Consequence of loop

   Current becomes the node at position pos, so current.next is undefined, causing error on insertion.

3. Final Answer:

   The loop runs one step too many, causing current to be null before insertion -> Option A

4. Quick Check:

   Loop overshoot breaks insertion [OK]

Hint: Loop to node before position, not at position [OK]

Common Mistakes:

• Looping to position instead of position-1
• Not checking for position 1 insertion
• Incorrectly updating links

5. Given a singly linked list and a position that may be greater than the list length, how should you modify the insertAtPosition function to insert the new node at the end if the position is beyond the list length? Choose the correct approach.

hard

A. Insert the new node at the head regardless of position

B. Throw an error if position is greater than list length

C. Traverse until current.next is null or position reached, then insert new node at current.next

D. Ignore the insertion if position is invalid

Solution

1. Step 1: Traverse safely

   Move current node forward until either position-1 steps or current.next is null (end of list).

2. Step 2: Insert at end if position too large

   If position is beyond length, current.next will be null, so insert new node at end by setting current.next to new node.

3. Final Answer:

   Traverse until current.next is null or position reached, then insert new node at current.next -> Option C

4. Quick Check:

   Insert at end if position too large [OK]

Hint: Stop at end or position, then insert [OK]

Common Mistakes:

• Not handling position beyond length
• Throwing error unnecessarily
• Inserting at wrong place when position invalid