Spiral Matrix Traversal in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the starting row index for spiral traversal.

DSA Typescript

let top = [1];

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

Amatrix.length

B1

C-1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Starting top at 1 instead of 0 causes skipping the first row.

Using matrix.length as top index causes out-of-bound errors.

The top row index starts at 0 because matrix indexing begins at 0.

2fill in blank

medium

Complete the code to move the left boundary inward after traversing the left column.

DSA Typescript

left [1]= 1;

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

A+

B*

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-=' decreases the left boundary, causing infinite loops.

Using '*' or '/' operators are incorrect for index movement.

We increase the left boundary by 1 to move it inward after traversing the left column.

3fill in blank

hard

Fix the error in the loop condition to correctly traverse the top row from left to right.

DSA Typescript

for (let i = left; i [1]= right; i++) {
  result.push(matrix[top][i]);
}

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

A<

B<=

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' excludes the last element in the top row.

Using '>' or '>=' causes the loop to never run.

The loop must include the right boundary, so use '<=' to include the last column.

4fill in blank

hard

Fill both blanks to correctly traverse the right column from top to bottom.

DSA Typescript

for (let i = [1]; i [2]= bottom; i++) {
  result.push(matrix[i][right]);
}

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

Atop

Bbottom

C<=

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Starting from bottom or using '>=' causes incorrect traversal direction.

Using '<' excludes the bottom row element.

The traversal starts at the top row and continues while i is less than or equal to bottom row.

5fill in blank

hard

Fill all three blanks to correctly traverse the bottom row from right to left.

DSA Typescript

for (let i = [1]; i [2] [3]; i--) {
  result.push(matrix[bottom][i]);
}

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

Aright

Bleft

C>=

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' causes the loop to never run when decrementing.

Starting from left or using '<' causes wrong traversal direction.

The loop starts at the right boundary, continues while i is greater than or equal to left, and moves leftwards by decrementing i.

Practice

1. What is the main idea behind Spiral Matrix Traversal?

easy

A. Traverse the matrix in a circular pattern starting from the outer layer moving inward

B. Traverse the matrix row by row from top to bottom

C. Traverse the matrix column by column from left to right

D. Traverse only the diagonal elements of the matrix

Solution

1. Step 1: Understand traversal pattern

   Spiral traversal means moving around the edges of the matrix first, then moving inward layer by layer.

2. Step 2: Compare options

   Only Traverse the matrix in a circular pattern starting from the outer layer moving inward describes this circular, inward movement. Others describe linear or diagonal traversals.

3. Final Answer:

   Traverse the matrix in a circular pattern starting from the outer layer moving inward -> Option A

4. Quick Check:

   Spiral traversal = circular inward movement [OK]

Hint: Think of peeling an onion layer by layer [OK]

Common Mistakes:

• Confusing spiral with row-wise traversal
• Thinking spiral means diagonal only
• Ignoring inward movement after outer layer

2. Which of the following TypeScript code snippets correctly initializes variables for spiral traversal boundaries?

easy

A. let top = -1, bottom = matrix.length - 1, left = -1, right = matrix[0].length - 1;

B. let top = 1, bottom = matrix.length, left = 1, right = matrix[0].length;

C. let top = 0, bottom = matrix.length, left = 0, right = matrix[0].length;

D. let top = 0, bottom = matrix.length - 1, left = 0, right = matrix[0].length - 1;

Solution

1. Step 1: Identify correct boundary initialization

   Top and left start at 0 (first row and column). Bottom and right are last indices, so length - 1.

2. Step 2: Check options

   let top = 0, bottom = matrix.length - 1, left = 0, right = matrix[0].length - 1; correctly sets top=0, bottom=rows-1, left=0, right=cols-1. Others have off-by-one or negative values.

3. Final Answer:

   let top = 0, bottom = matrix.length - 1, left = 0, right = matrix[0].length - 1; -> Option D

4. Quick Check:

   Boundaries start at 0 and end at length-1 [OK]

Hint: Remember array indices start at 0 [OK]

Common Mistakes:

• Using length instead of length - 1 for boundaries
• Starting top or left at 1 instead of 0
• Using negative indices incorrectly

3. Given a rectangular matrix with 3 rows and 5 columns, how many elements will be printed after a complete spiral traversal?

easy

A. 15

B. 8

C. 12

D. 10

Solution

1. Step 1: Calculate total elements in matrix

   Number of elements = rows x columns = 3 x 5 = 15.

2. Step 2: Understand spiral traversal covers all elements

   Spiral traversal visits every element exactly once, so all 15 elements are printed.

3. Final Answer:

   15 -> Option A

4. Quick Check:

   Total elements = rows x columns = 15 [OK]

Hint: Spiral prints all elements once [OK]

Common Mistakes:

• Confusing spiral length with perimeter
• Counting only outer layer elements
• Ignoring rectangular shape

4. What is the output of the following TypeScript code for spiral traversal?

const matrix = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
];

function spiralOrder(matrix: number[][]): number[] {
  const result: number[] = [];
  let top = 0, bottom = matrix.length - 1;
  let left = 0, right = matrix[0].length - 1;

  while (top <= bottom && left <= right) {
    for (let i = left; i <= right; i++) result.push(matrix[top][i]);
    top++;
    for (let i = top; i <= bottom; i++) result.push(matrix[i][right]);
    right--;
    if (top <= bottom) {
      for (let i = right; i >= left; i--) result.push(matrix[bottom][i]);
      bottom--;
    }
    if (left <= right) {
      for (let i = bottom; i >= top; i--) result.push(matrix[i][left]);
      left++;
    }
  }
  return result;
}

console.log(spiralOrder(matrix));

medium

A. [1, 4, 7, 8, 9, 6, 3, 2, 5]

B. [1, 2, 3, 6, 9, 8, 7, 4, 5]

C. [1, 2, 3, 4, 5, 6, 7, 8, 9]

D. [9, 8, 7, 4, 1, 2, 3, 6, 5]

Solution

1. Step 1: Trace the spiral traversal on the matrix

   Start top row left to right: 1,2,3
   Right column top to bottom: 6,9
   Bottom row right to left: 8,7
   Left column bottom to top: 4
   Now inner layer: 5

2. Step 2: Combine all elements in order

   Result array: [1,2,3,6,9,8,7,4,5]

3. Final Answer:

   [1, 2, 3, 6, 9, 8, 7, 4, 5] -> Option B

4. Quick Check:

   Spiral order matches [1, 2, 3, 6, 9, 8, 7, 4, 5] [OK]

Hint: Visualize peeling matrix edges in order [OK]

Common Mistakes:

• Reading rows only left to right
• Skipping inner elements
• Mixing traversal directions

5. Identify the bug in this spiral traversal code snippet:

while (top < bottom && left < right) {
  for (let i = left; i <= right; i++) result.push(matrix[top][i]);
  top++;
  for (let i = top; i <= bottom; i++) result.push(matrix[i][right]);
  right--;
  for (let i = right; i >= left; i--) result.push(matrix[bottom][i]);
  bottom--;
  for (let i = bottom; i >= top; i--) result.push(matrix[i][left]);
  left++;
}

medium

A. The for loops should use < instead of <= to avoid index out of bounds

B. The variables top, bottom, left, right are not initialized

C. The while loop condition should use <= instead of < to include last row and column

D. The result array is not declared before the loop

Solution

1. Step 1: Analyze the while loop condition

   Using < excludes the last row and column when top == bottom or left == right, missing elements.

2. Step 2: Correct the condition

   Change while (top < bottom && left < right) to while (top <= bottom && left <= right) to include all layers.

3. Final Answer:

   The while loop condition should use <= instead of < to include last row and column -> Option C

4. Quick Check:

   Use <= in loop condition to cover all edges [OK]

Hint: Use <= to include boundary rows and columns [OK]

Common Mistakes:

• Using < excludes last layer elements
• Not updating boundaries inside loop
• Forgetting to check conditions before loops