Array iteration and enumerated in Swift - Time & Space Complexity

Time Complexity: Array iteration and enumerated

O(n)

Understanding Time Complexity

When we loop through an array using iteration and the enumerated method, we want to know how the time it takes grows as the array gets bigger.

We ask: How does the number of steps change when the array size increases?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

let numbers = [10, 20, 30, 40, 50]
for (index, value) in numbers.enumerated() {
    print("Index: \(index), Value: \(value)")
}
    

This code goes through each item in the array and prints its position and value.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Looping through each element of the array once.
• How many times: Exactly once for each element, so as many times as the array length.

How Execution Grows With Input

As the array gets bigger, the number of steps grows directly with the number of items.

Input Size (n)	Approx. Operations
10	10 steps
100	100 steps
1000	1000 steps

Pattern observation: The steps increase evenly as the array size grows.

Final Time Complexity

Time Complexity: O(n)

This means the time to finish grows in a straight line with the number of items in the array.

Common Mistake

[X] Wrong: "Using enumerated makes the loop slower because it adds extra work."

[OK] Correct: Enumerated just pairs each item with its index during the same single pass, so it does not add extra loops or slow down the process noticeably.

Interview Connect

Understanding how simple loops grow with input size helps you explain your code clearly and shows you know how to think about efficiency in real projects.

Self-Check

"What if we nested another loop inside to compare each element with every other element? How would the time complexity change?"

Practice

1. What does the enumerated() method do when used on an array in Swift?

easy

A. It provides both the index and the value of each element during iteration.

B. It reverses the order of the array elements.

C. It filters out duplicate elements from the array.

D. It sorts the array in ascending order.

Solution

1. Step 1: Understand the purpose of enumerated()

   The enumerated() method returns a sequence of pairs (index, value) for each element in the array.

2. Step 2: Identify what is returned during iteration

   Each iteration gives you the position (index) and the element itself (value), allowing you to use both.

3. Final Answer:

   It provides both the index and the value of each element during iteration. -> Option A

4. Quick Check:

   enumerated() = index + value [OK]

Hint: Remember: enumerated() gives index and item together [OK]

Common Mistakes:

• Thinking enumerated() changes array order
• Believing enumerated() filters or sorts elements
• Confusing enumerated() with map or filter

2. Which of the following is the correct syntax to iterate over an array fruits using enumerated() in Swift?

easy

A. for (index, fruit) in fruits.enumerated() { print(index, fruit) }

B. for index, fruit in fruits { print(index, fruit) }

C. for index, fruit in fruits.enumerated { print(index, fruit) }

D. for (fruit, index) in fruits.enumerated() { print(index, fruit) }

Solution

1. Step 1: Check the correct use of enumerated()

   The method enumerated() must be called with parentheses to return the sequence.

2. Step 2: Verify tuple unpacking syntax

   The for loop must unpack the tuple as (index, value) in parentheses.

3. Final Answer:

   for (index, fruit) in fruits.enumerated() { print(index, fruit) } -> Option A

4. Quick Check:

   Correct syntax = for (index, fruit) in fruits.enumerated() { print(index, fruit) } [OK]

Hint: Use parentheses with enumerated() and tuple unpacking [OK]

Common Mistakes:

• Omitting parentheses after enumerated()
• Swapping index and value order in tuple
• Trying to unpack without parentheses

3. What will be the output of the following Swift code?

let animals = ["cat", "dog", "bird"]
for (i, animal) in animals.enumerated() {
    print("\(i): \(animal)")
}

medium

A. cat: 0
dog: 1
bird: 2

B. 1: cat
2: dog
3: bird

C. 0: cat
1: dog
2: bird

D. cat
dog
bird

Solution

1. Step 1: Understand enumerated() output

   enumerated() gives index starting at 0 and the element value.

2. Step 2: Trace the print statements

   Each line prints index, colon, space, then the animal name.

3. Final Answer:

   0: cat 1: dog 2: bird -> Option C

4. Quick Check:

   Index starts at 0, prints index: value [OK]

Hint: Indexes start at 0 unless adjusted [OK]

Common Mistakes:

• Assuming index starts at 1
• Printing value before index
• Ignoring the colon and space formatting

4. Identify the error in the following Swift code snippet:

let numbers = [10, 20, 30]
for index, value in numbers.enumerated {
    print(index, value)
}

medium

A. print statement syntax is invalid.

B. Incorrect variable names in the for loop.

C. Array declaration syntax is wrong.

D. Missing parentheses after enumerated() method call.

Solution

1. Step 1: Check method call syntax

   The method enumerated must be called with parentheses: enumerated().

2. Step 2: Verify other parts of the code

   Variable names and array declaration are correct; print syntax is valid.

3. Final Answer:

   Missing parentheses after enumerated() method call. -> Option D

4. Quick Check:

   enumerated() needs () [OK]

Hint: Always add () after enumerated [OK]

Common Mistakes:

• Forgetting parentheses after enumerated
• Swapping index and value order
• Using wrong print syntax

5. Given an array scores = [85, 92, 78, 90], write Swift code using enumerated() to print each score with its position starting from 1, like "Player 1: 85". Which code snippet correctly does this?

hard

A. for score in scores { print("Player \(score): \(score)") }

B. for (index, score) in scores.enumerated() { print("Player \(index + 1): \(score)") }

C. for (index, score) in scores.enumerated() { print("Player \(index): \(score)") }

D. for (score, index) in scores.enumerated() { print("Player \(index + 1): \(score)") }

Solution

1. Step 1: Use enumerated() to get index and score

   enumerated() returns (index, value) tuples; index starts at 0.

2. Step 2: Adjust index to start from 1 in print

   Add 1 to index when printing to start counting players from 1.

3. Final Answer:

   for (index, score) in scores.enumerated() { print("Player \(index + 1): \(score)") } -> Option B

4. Quick Check:

   Index + 1 for counting players [OK]

Hint: Add 1 to index to start counting from 1 [OK]

Common Mistakes:

• Printing index without adding 1
• Swapping index and value in tuple
• Using wrong tuple unpacking order