Range operators (... and ..<) in Swift - Time & Space Complexity

Time Complexity: Range operators (... and ..<)

O(n)

Understanding Time Complexity

When using Swift's range operators, it is important to know how the number of steps grows as the range size increases.

We want to understand how the time to process a range changes when the range gets bigger.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

let n = 100
for i in 0...n {
    print(i)
}

This code prints numbers from 0 up to n using the closed range operator (...).

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The for-loop runs once for each number in the range.
• How many times: It runs n + 1 times because the range includes both 0 and n.

How Execution Grows With Input

As n grows, the number of times the loop runs grows almost the same way.

Input Size (n)	Approx. Operations
10	11
100	101
1000	1001

Pattern observation: The operations increase roughly one by one as n increases.

Final Time Complexity

Time Complexity: O(n)

This means the time to run the loop grows in direct proportion to the size of the range.

Common Mistake

[X] Wrong: "The loop runs a fixed number of times no matter how big n is."

[OK] Correct: The loop runs once for each number in the range, so if n grows, the loop runs more times.

Interview Connect

Understanding how loops over ranges grow helps you explain how your code handles bigger inputs clearly and confidently.

Self-Check

"What if we changed the closed range operator (...) to the half-open range operator (..<)? How would the time complexity change?"

Practice

1. What does the Swift range operator 1...5 represent?

easy

A. A range including numbers 1, 2, 3, 4, and 5

B. A range including numbers 1, 2, 3, and 4 only

C. A range excluding number 1 but including 5

D. A range excluding both 1 and 5

Solution

1. Step 1: Understand the closed range operator

   The ... operator creates a range that includes both the start and end values.

2. Step 2: Apply to the given range

   For 1...5, it includes 1, 2, 3, 4, and 5.

3. Final Answer:

   A range including numbers 1, 2, 3, 4, and 5 -> Option A

4. Quick Check:

   1...5 includes 5 [OK]

Hint: Remember: ... includes end number, ..< excludes it [OK]

Common Mistakes:

• Thinking ... excludes the last number
• Confusing ... with ..<
• Assuming ..< includes the end number

2. Which of the following is the correct syntax to create a half-open range from 0 to 9 in Swift?

easy

A. 0...9

B. 0..<10

C. 0..9

D. 0...10

Solution

1. Step 1: Identify half-open range syntax

   The half-open range operator in Swift is ..<, which includes the start but excludes the end.

2. Step 2: Apply to the range 0 to 9

   To include numbers 0 through 9, use 0..<10 because 10 is excluded.

3. Final Answer:

   0..<10 -> Option B

4. Quick Check:

   ..< excludes end [OK]

Hint: Use ..< to exclude the last number in range [OK]

Common Mistakes:

• Using ... when half-open range is needed
• Writing 0..9 which is invalid syntax
• Confusing end number inclusion

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

for i in 3..<6 {
    print(i, terminator: ",")
}

medium

A. 3,4,5,6,

B. 4,5,6,

C. 3,4,5,

D. 3,4,5,6

Solution

1. Step 1: Understand the range used in the loop

   The range 3..<6 includes 3, 4, and 5 but excludes 6.

2. Step 2: Trace the loop output

   The loop prints 3, then 4, then 5, each followed by a comma.

3. Final Answer:

   3,4,5, -> Option C

4. Quick Check:

   ..<6 excludes 6 [OK]

Hint: ..< excludes end; loop stops before 6 [OK]

Common Mistakes:

• Including 6 in output
• Missing commas in output
• Confusing terminator usage

4. The following Swift code has an error. What is the problem?

let range = 1..5
for num in range {
    print(num)
}

medium

A. The range operator .. is invalid in Swift

B. The loop variable num is not declared

C. The print statement syntax is incorrect

D. The range should start from 0

Solution

1. Step 1: Check the range operator used

   The code uses 1..5, which is not a valid range operator in Swift.

2. Step 2: Identify correct range operators

   Swift uses ... for closed ranges and ..< for half-open ranges, but not ...

3. Final Answer:

   The range operator .. is invalid in Swift -> Option A

4. Quick Check:

   Invalid operator .. causes error [OK]

Hint: Use ... or ..<, never .. alone [OK]

Common Mistakes:

• Using .. instead of ... or ..<
• Assuming .. is a valid operator
• Ignoring compiler error messages

5. You want to create a Swift array containing numbers from 5 to 15, excluding 15, and then print only the even numbers. Which code snippet correctly uses range operators and filtering?

hard

A. let numbers = Array(5...15).filter { $0 % 2 == 0 }
print(numbers)

B. let numbers = Array(5..15).filter { $0 % 2 == 0 }
print(numbers)

C. let numbers = Array(5..<14).filter { $0 % 2 == 0 }
print(numbers)

D. let numbers = Array(5..<15).filter { $0 % 2 == 0 }
print(numbers)

Solution

1. Step 1: Choose correct range excluding 15

   To exclude 15, use the half-open range 5..<15, which includes 5 up to 14.

2. Step 2: Filter even numbers

   The filter condition { $0 % 2 == 0 } selects even numbers from the array.

3. Step 3: Verify other options

   let numbers = Array(5...15).filter { $0 % 2 == 0 } print(numbers) includes 15, let numbers = Array(5..15).filter { $0 % 2 == 0 } print(numbers) uses invalid operator .., and let numbers = Array(5..<14).filter { $0 % 2 == 0 } print(numbers) uses 5..<14 which goes only up to 13, missing the even number 14.

4. Final Answer:

   let numbers = Array(5..<15).filter { $0 % 2 == 0 } print(numbers) -> Option D

5. Quick Check:

   ..< excludes end, filter selects even [OK]

Hint: Use ..< to exclude end, then filter even numbers [OK]

Common Mistakes:

• Using ... to include 15 mistakenly
• Using invalid .. operator
• Not filtering correctly for even numbers