Traversal Forward and Backward in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to traverse the array forward and print each element.

DSA Typescript

const arr = [1, 2, 3, 4, 5];
for (let i = 0; i [1] arr.length; i++) {
  console.log(arr[i]);
}

Drag options to blanks, or click blank then click option'

A<

B>=

C<=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using <= causes an index out of range error.

Using > or >= will not enter the loop.

The loop should run while i is less than the array length to avoid going out of bounds.

2fill in blank

medium

Complete the code to traverse the array backward and print each element except the first one.

DSA Typescript

const arr = [1, 2, 3, 4, 5];
for (let i = arr.length - 1; i [1] 0; i--) {
  console.log(arr[i]);
}

Drag options to blanks, or click blank then click option'

A>=

B<

C>

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using >= 0 will include index 0, so the loop should use > 0 to exclude it.

Using < or <= will not run the loop backward.

The loop should continue while i is greater than 0 to include all elements except index 0.

3fill in blank

hard

Fix the error in the backward traversal loop condition to include the first element.

DSA Typescript

const arr = [10, 20, 30, 40];
for (let i = arr.length - 1; i [1] 0; i--) {
  console.log(arr[i]);
}

Drag options to blanks, or click blank then click option'

A>=

B<

C>

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using > 0 excludes the first element.

Using < or <= will not work for backward traversal.

Using >= 0 ensures the loop includes the element at index 0.

4fill in blank

hard

Fill both blanks to create a forward traversal that prints only even numbers.

DSA Typescript

const nums = [1, 2, 3, 4, 5, 6];
for (let i = 0; i [1] nums.length; i++) {
  if (nums[i] [2] 2 === 0) {
    console.log(nums[i]);
  }
}

Drag options to blanks, or click blank then click option'

A<

B%

C===

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using > instead of < in the loop condition causes no iteration.

Using === instead of % for checking even numbers is incorrect.

The loop runs while i is less than the array length. The modulus operator % checks if the number is even.

5fill in blank

hard

Fill all three blanks to create a backward traversal that prints numbers greater than 3.

DSA Typescript

const values = [2, 4, 6, 1, 5];
for (let i = values.length - 1; i [1] 0; i--) {
  if (values[i] [2] 3) {
    console.log(values[[3]]);
  }
}

Drag options to blanks, or click blank then click option'

A>=

B>

Ci

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using > 0 excludes the first element.

Using < instead of > in the condition prints wrong elements.

Using wrong index inside console.log causes errors.

The loop continues while i is greater than or equal to 0. The condition checks if the value is greater than 3. The index i is used to access the array element.

Practice

1. What does forward traversal in a linked list mean?

easy

A. Visiting nodes randomly without order

B. Visiting nodes from the tail to the head in order

C. Skipping every other node while traversing

D. Visiting nodes from the head to the tail in order

Solution

1. Step 1: Understand linked list structure

   A linked list has nodes connected from head to tail in one direction.

2. Step 2: Define forward traversal

   Forward traversal means visiting nodes starting at the head and moving to the tail in order.

3. Final Answer:

   Visiting nodes from the head to the tail in order -> Option D

4. Quick Check:

   Forward traversal = head to tail [OK]

Hint: Forward means start at head and go next nodes [OK]

Common Mistakes:

• Confusing forward with backward traversal
• Thinking traversal is random
• Assuming skipping nodes is traversal

2. Which TypeScript syntax correctly traverses an array forward using a for loop?

easy

A. for(let i = arr.length; i >= 0; i--) { console.log(arr[i]); }

B. for(let i = 0; i < arr.length; i++) { console.log(arr[i]); }

C. for(let i = 1; i <= arr.length; i++) { console.log(arr[i]); }

D. for(let i = arr.length - 1; i > 0; i--) { console.log(arr[i]); }

Solution

1. Step 1: Identify forward traversal loop

   Forward traversal starts at index 0 and goes up to length-1.

2. Step 2: Check loop conditions

   for(let i = 0; i < arr.length; i++) { console.log(arr[i]); } loops from 0 to less than arr.length, printing each element correctly.

3. Final Answer:

   for(let i = 0; i < arr.length; i++) { console.log(arr[i]); } -> Option B

4. Quick Check:

   Forward loop index from 0 to length-1 [OK]

Hint: Start index 0, end before length for forward loop [OK]

Common Mistakes:

• Starting index at 1 instead of 0
• Using i <= arr.length causing out-of-bounds
• Looping backward for forward traversal

3. What is the output of this TypeScript code?

const arr = [10, 20, 30];
for(let i = arr.length - 1; i >= 0; i--) {
  console.log(arr[i]);
}

medium

A. 30 20 10

B. 10 20 30

C. 30 20

D. Error: Index out of bounds

Solution

1. Step 1: Understand loop start and end

   The loop starts at index 2 (arr.length - 1) and goes down to 0.

2. Step 2: Trace output values

   It prints arr[2] = 30, arr[1] = 20, arr[0] = 10 in that order.

3. Final Answer:

   30 20 10 -> Option A

4. Quick Check:

   Backward traversal prints 30 20 10 [OK]

Hint: Backward loop starts at length-1 down to 0 [OK]

Common Mistakes:

• Thinking output is forward order
• Missing last element at index 0
• Assuming error due to loop

4. Identify the error in this backward traversal code for a linked list:

let current = head;
while(current !== null) {
  console.log(current.value);
  current = current.prev;
}

medium

A. It should use current.next instead of current.prev

B. No error, code is correct

C. It should start from tail, not head

D. It should check current.next !== null in while condition

Solution

1. Step 1: Understand backward traversal in linked list

   Backward traversal uses prev pointers starting from the tail node.

2. Step 2: Check starting node

   The code starts at head, but to go backward, it must start at tail.

3. Final Answer:

   It should start from tail, not head -> Option C

4. Quick Check:

   Backward traversal starts at tail [OK]

Hint: Backward traversal must start at tail node [OK]

Common Mistakes:

• Starting backward traversal at head
• Using next instead of prev for backward
• Wrong loop condition check

5. Given a doubly linked list, how would you print all values backward starting from the head node?

hard

A. Traverse forward to tail, then traverse backward from tail to head

B. Traverse backward directly from head using prev pointers

C. Use only next pointers starting from head to print backward

D. Reverse the list first, then traverse forward

Solution

1. Step 1: Understand doubly linked list structure

   Each node has next and prev pointers; head has no prev, tail has no next.

2. Step 2: Plan backward print from head

   To print backward from head, first move forward to tail using next pointers.

3. Step 3: Traverse backward from tail

   From tail, use prev pointers to print nodes backward to head.

4. Final Answer:

   Traverse forward to tail, then traverse backward from tail to head -> Option A

5. Quick Check:

   Backward print from head requires forward then backward traversal [OK]

Hint: Go forward to tail, then backward to print [OK]

Common Mistakes:

• Trying to go backward directly from head
• Using next pointers to print backward
• Reversing list unnecessarily