Array Traversal Patterns in DSA Python - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Nested Loop Traversal

What is the output of the following code that traverses a 2D array row-wise?

DSA Python

arr = [[1, 2], [3, 4]]
result = []
for row in arr:
    for val in row:
        result.append(val)
print(result)

A [[1, 2], [3, 4]]

B [1, 3, 2, 4]

C [1, 2, 3, 4]

D [4, 3, 2, 1]

💡 Hint

Think about how nested loops go through each element in order.

The outer loop goes row by row, and the inner loop goes through each element in the row, so the elements are added in order: 1, 2, 3, 4.

❓ Predict Output

intermediate

Output of Reverse Array Traversal

What is the output of this code that traverses an array backwards?

DSA Python

arr = [10, 20, 30, 40]
result = []
for i in range(len(arr)-1, -1, -1):
    result.append(arr[i])
print(result)

A [40, 30, 20, 10]

B [10, 20, 30, 40]

C [40, 20, 30, 10]

D [30, 40, 20, 10]

💡 Hint

The loop starts from the last index and goes to the first.

The loop goes from the last element to the first, so the result is the reversed array.

🔧 Debug

advanced

Identify the Error in Diagonal Traversal

What error does this code produce when trying to traverse the main diagonal of a square matrix?

DSA Python

matrix = [[1,2,3],[4,5,6],[7,8,9]]
for i in range(len(matrix)):
    print(matrix[i][i+1])

A No error, prints diagonal elements

B TypeError: unsupported operand type(s)

C SyntaxError: invalid syntax

D IndexError: list index out of range

💡 Hint

Check the index used inside the loop for accessing elements.

The code tries to access matrix[i][i+1], which goes out of range when i is at the last index.

🧠 Conceptual

advanced

Number of Elements Visited in Zigzag Traversal

Given a 3x3 matrix, how many elements are visited if we traverse it in a zigzag pattern row-wise (left to right on first row, right to left on second, and so on)?

A 9

B 6

C 3

D 12

💡 Hint

Zigzag means visiting every element but changing direction each row.

All elements are visited once, just the order changes, so total is 9.

🚀 Application

expert

Output After Spiral Traversal of 3x3 Matrix

What is the output list after performing a spiral traversal on this 3x3 matrix? matrix = [[1,2,3],[4,5,6],[7,8,9]]

DSA Python

def spiral_traversal(matrix):
    result = []
    top, bottom = 0, len(matrix) - 1
    left, right = 0, len(matrix[0]) - 1
    while left <= right and top <= bottom:
        for i in range(left, right + 1):
            result.append(matrix[top][i])
        top += 1
        for i in range(top, bottom + 1):
            result.append(matrix[i][right])
        right -= 1
        if top <= bottom:
            for i in range(right, left - 1, -1):
                result.append(matrix[bottom][i])
            bottom -= 1
        if left <= right:
            for i in range(bottom, top - 1, -1):
                result.append(matrix[i][left])
            left += 1
    return result

print(spiral_traversal(matrix))

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

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

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

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

💡 Hint

Spiral traversal goes around the edges inward in a clockwise direction.

The spiral order visits top row left to right, right column top to bottom, bottom row right to left, left column bottom to top, then repeats inward.