Repeat function for simple repetition in Kotlin - Time & Space Complexity

Time Complexity: Repeat function for simple repetition

O(n)

Understanding Time Complexity

We want to understand how the time taken by Kotlin's repeat function changes as we repeat an action more times.

The question is: How does the number of repetitions affect the total work done?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

fun printHello(times: Int) {
    repeat(times) {
        println("Hello")
    }
}

printHello(5)
    

This code prints "Hello" a number of times given by times.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The repeat function runs the print statement multiple times.
• How many times: Exactly times times, as given by the input.

How Execution Grows With Input

Each time we increase times, the print action happens that many more times.

Input Size (times)	Approx. Operations (prints)
10	10
100	100
1000	1000

Pattern observation: The number of operations grows directly with the input size.

Final Time Complexity

Time Complexity: O(n)

This means if you double the number of repetitions, the total work roughly doubles too.

Common Mistake

[X] Wrong: "The repeat function runs instantly no matter how many times."

[OK] Correct: Each repetition runs the code inside once, so more repetitions mean more work and more time.

Interview Connect

Understanding how simple loops like repeat scale helps you explain how programs handle repeated tasks efficiently.

Self-Check

"What if we nested one repeat inside another? How would the time complexity change?"

Practice

1. What does the Kotlin repeat function do?

easy

A. Defines a loop that runs until a condition is false

B. Repeats a string multiple times

C. Runs a block of code a specified number of times

D. Creates a list with repeated elements

Solution

1. Step 1: Understand the purpose of repeat

   The repeat function is designed to run a block of code a fixed number of times.

2. Step 2: Compare with other options

   Options B and C describe string or list repetition, which are different functions. Defines a loop that runs until a condition is false describes a conditional loop, not repeat.

3. Final Answer:

   Runs a block of code a specified number of times -> Option C

4. Quick Check:

   repeat = run code N times [OK]

Hint: Remember: repeat runs code block N times [OK]

Common Mistakes:

• Confusing repeat with string repetition
• Thinking repeat creates collections
• Mixing repeat with while or for loops

2. Which of the following is the correct syntax to repeat a print statement 3 times in Kotlin?

easy

A. repeat 3 { println("Hello") }

B. repeat(3) { println("Hello") }

C. repeat(3); println("Hello")

D. repeat {3} println("Hello")

Solution

1. Step 1: Check the function call syntax

   The repeat function requires parentheses around the number of repetitions and a lambda block with curly braces.

2. Step 2: Validate each option

   repeat(3) { println("Hello") } correctly uses repeat(3) { ... }. Options B, C, and D have syntax errors or misplaced braces.

3. Final Answer:

   repeat(3) { println("Hello") } -> Option B

4. Quick Check:

   repeat(number) { code } syntax [OK]

Hint: Use parentheses for count and braces for code block [OK]

Common Mistakes:

• Omitting parentheses around the count
• Using semicolon instead of braces
• Placing braces incorrectly

3. What will be the output of this Kotlin code?

repeat(4) { i -> println(i * 2) }

medium

A. 0 1 2 3

B. 2 4 6 8

C. 1 2 3 4

D. 0 2 4 6

Solution

1. Step 1: Understand the index parameter

   The lambda receives i from 0 to 3 (4 times). Each iteration prints i * 2.

2. Step 2: Calculate each output line

   For i=0: 0*2=0, i=1: 2, i=2: 4, i=3: 6. So output lines are 0, 2, 4, 6.

3. Final Answer:

   0 2 4 6 -> Option D

4. Quick Check:

   repeat with index * 2 = 0 2 4 6 [OK]

Hint: Index starts at 0 in repeat lambda [OK]

Common Mistakes:

• Starting index at 1 instead of 0
• Forgetting to multiply by 2
• Confusing output with index values

4. Identify the error in this Kotlin code:

repeat(3) 
 println("Hi")

medium

A. Missing curly braces for the code block

B. repeat cannot be used with println

C. repeat requires a semicolon after the number

D. The number 3 should be a string

Solution

1. Step 1: Check the syntax of repeat

   The repeat function expects a lambda block enclosed in curly braces after the count.

2. Step 2: Identify the missing braces

   The code has no braces around println("Hi"), so it is a syntax error.

3. Final Answer:

   Missing curly braces for the code block -> Option A

4. Quick Check:

   repeat needs braces { } for code [OK]

Hint: Always use braces { } after repeat(count) [OK]

Common Mistakes:

• Omitting braces for single statement
• Adding semicolon after number
• Passing number as string

5. How can you use repeat to create a list of squares of numbers from 0 to 4 in Kotlin?

hard

A. val squares = mutableListOf<Int>(); repeat(5) { squares.add(it * it) }

B. val squares = repeat(5) { it * it }

C. val squares = List(5) { repeat(it * it) }

D. val squares = repeat(5) { println(it * it) }

Solution

1. Step 1: Understand repeat usage for list building

   The repeat function runs code multiple times but does not return a list itself.

2. Step 2: Check each option's approach

   val squares = mutableListOf<Int>(); repeat(5) { squares.add(it * it) } creates a mutable list and adds squares inside repeat, which works. val squares = repeat(5) { it * it } tries to assign repeat's result directly, which is Unit (no list). val squares = List(5) { repeat(it * it) } misuses List and repeat. val squares = repeat(5) { println(it * it) } only prints values, no list created.

3. Final Answer:

   val squares = mutableListOf<Int>(); repeat(5) { squares.add(it * it) } -> Option A

4. Quick Check:

   repeat + add to list = correct list [OK]

Hint: Use repeat to add items to a mutable list [OK]

Common Mistakes:

• Expecting repeat to return a list
• Using repeat inside List constructor incorrectly
• Only printing values without storing