Repeat loop with break in R Programming - Time & Space Complexity

Time Complexity: Repeat loop with break

O(n)

Understanding Time Complexity

We want to understand how long a repeat loop with a break runs as the input size changes.

Specifically, how many times does the loop repeat before it stops?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

i <- 1
repeat {
  if (i > n) {
    break
  }
  print(i)
  i <- i + 1
}
    

This code counts from 1 up to n, printing each number, then stops.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The repeat loop that prints numbers.
• How many times: It runs once for each number from 1 to n, so n times.

How Execution Grows With Input

As n gets bigger, the loop runs more times, directly matching n.

Input Size (n)	Approx. Operations
10	About 10 repeats
100	About 100 repeats
1000	About 1000 repeats

Pattern observation: The number of repeats grows evenly as n grows.

Final Time Complexity

Time Complexity: O(n)

This means the time to finish grows directly with the size of n.

Common Mistake

[X] Wrong: "The repeat loop always runs forever because it has no set end."

[OK] Correct: The break condition stops the loop once i passes n, so it does end after n repeats.

Interview Connect

Understanding how loops with breaks behave helps you explain how code runs step-by-step and how long it takes.

Self-Check

"What if the break condition checked for i > n^2 instead? How would the time complexity change?"

Practice

1.

What does the repeat loop do in R?

Choose the best description.

easy

A. It runs code only once and then stops automatically.

B. It runs code repeatedly until a break statement stops it.

C. It runs code a fixed number of times without stopping early.

D. It runs code only if a condition is true at the start.

Solution

1. Step 1: Understand the repeat loop behavior and compare options

   The repeat loop in R runs indefinitely until a break is encountered. Only "It runs code repeatedly until a break statement stops it." correctly describes that the loop runs repeatedly until break stops it.

2. Final Answer:

   It runs code repeatedly until a break statement stops it. -> Option B

3. Quick Check:

   repeat loop = runs until break [OK]

Hint: Remember: repeat loops run forever until break stops them [OK]

Common Mistakes:

• Thinking repeat loops run a fixed number of times
• Confusing repeat with for or while loops
• Assuming repeat loops stop automatically without break

2.

Which of the following is the correct syntax to start a repeat loop in R?

?

easy

A. repeat { }

B. repeat() { }

C. repeat[] { }

D. repeat do { }

Solution

1. Step 1: Recall the syntax of repeat loops in R and check options

   The correct syntax is repeat { ... } without parentheses or other symbols. Only repeat { } matches the correct syntax exactly.

2. Final Answer:

   repeat { } -> Option A

3. Quick Check:

   repeat loop syntax = repeat { } [OK]

Hint: repeat loops use braces {} without parentheses [OK]

Common Mistakes:

• Adding parentheses after repeat
• Using square brackets instead of braces
• Using keywords like do with repeat

3.

What will be the output of this R code?

i <- 1
repeat {
  if (i > 3) break
  print(i)
  i <- i + 1
}

medium

A. No output, infinite loop

B. [1] 1
[1] 2
[1] 3
[1] 4

C. [1] 1
[1] 2

D. [1] 1
[1] 2
[1] 3

Solution

1. Step 1: Trace the loop iterations

   i starts at 1. Loop checks if i > 3, breaks if true. Otherwise, prints i and increments i by 1. When i becomes 4, condition i > 3 is true, so break stops the loop. Values printed are 1, 2, and 3 before break.

2. Final Answer:

   [1] 1 [1] 2 [1] 3 -> Option D

3. Quick Check:

   Prints 1 to 3 then breaks [OK]

Hint: Loop breaks when i > 3, so prints 1,2,3 only [OK]

Common Mistakes:

• Expecting it to print 4
• Thinking it runs infinitely
• Forgetting to increment i

4.

Find the error in this R code using repeat and break:

count <- 1
repeat {
  print(count)
  if (count == 5)
    break
}

medium

A. The variable count is never incremented, causing an infinite loop.

B. The break statement is outside the loop.

C. The repeat loop syntax is incorrect.

D. The if condition should be count > 5.

Solution

1. Step 1: Check loop variable changes and behavior

   The variable count is printed but never increased, so it stays 1 forever. Since count never reaches 5, break is never triggered, causing an infinite loop.

2. Final Answer:

   The variable count is never incremented, causing an infinite loop. -> Option A

3. Quick Check:

   Missing increment causes infinite loop [OK]

Hint: Always update loop variables to avoid infinite loops [OK]

Common Mistakes:

• Forgetting to increment the loop counter
• Misplacing the break statement
• Incorrect loop syntax assumptions

5.

Write a repeat loop in R that prints numbers from 10 down to 1 and then stops.

Which code snippet correctly does this?

?

hard

A. i <- 10
repeat {
print(i)
i <- i - 1
if (i < 0) break
}

B. i <- 10
repeat {
print(i)
i <- i + 1
if (i == 0) break
}

C. i <- 10
repeat {
print(i)
if (i == 1) break
i <- i - 1
}

D. i <- 1
repeat {
print(i)
i <- i + 1
if (i > 10) break
}

Solution

1. Step 1: Understand the counting direction and check options

   We want to print from 10 down to 1, then stop. So i starts at 10 and decreases by 1 each loop. i <- 10 repeat { print(i) i <- i - 1 if (i < 0) break } prints i, then decrements i, and breaks when i < 0, so it prints 10 down to 0 inclusive, but since break is after decrement, it stops after printing 0. To print 10 down to 1, break should be when i < 1. i <- 10 repeat { print(i) if (i == 1) break i <- i - 1 } prints i, breaks when i == 1, then decrements i, so it prints 10 down to 1 correctly and stops. Therefore, i <- 10 repeat { print(i) if (i == 1) break i <- i - 1 } is the correct code snippet.

2. Final Answer:

   i <- 10 repeat { print(i) if (i == 1) break i <- i - 1 } -> Option C

3. Quick Check:

   Counts down 10 to 1 then breaks [OK]

Hint: Break after printing 1 to include it in output [OK]

Common Mistakes:

• Breaking before printing 1, missing last number
• Incrementing instead of decrementing
• Wrong break condition causing infinite loop