Labeled break and continue in Javascript - Time & Space Complexity

Time Complexity: Labeled break and continue

O(n²)

Understanding Time Complexity

We want to see how using labeled break and continue affects how long a program takes to run.

Specifically, we ask: how does skipping or stopping loops early change the work done as input grows?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

outerLoop: for (let i = 0; i < n; i++) {
  for (let j = 0; j < n; j++) {
    if (j === i) continue outerLoop;
    if (i + j > n) break outerLoop;
  }
}
    

This code uses labeled break and continue to jump out of or skip parts of loops based on conditions.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Nested loops over i and j from 0 to n.
• How many times: Up to n times for outer loop, and up to n times for inner loop, but breaks and continues can stop inner loop early.

How Execution Grows With Input

As n grows, the loops try to run more times, but labeled break and continue can stop inner loops early.

Input Size (n)	Approx. Operations
10	Less than 100 due to early breaks
100	Less than 10,000 but more than 1,000
1000	Less than 1,000,000 but more than 100,000

Pattern observation: The work grows roughly with the square of n, but early exits reduce some work.

Final Time Complexity

Time Complexity: O(n²)

This means the time grows roughly like the square of the input size, even with labeled breaks and continues.

Common Mistake

[X] Wrong: "Using labeled break or continue always makes the code run in constant time."

[OK] Correct: Even though these statements can skip some work, the loops still mostly run many times as input grows, so time still grows with input size.

Interview Connect

Understanding how labeled break and continue affect loop execution helps you explain code efficiency clearly and confidently in interviews.

Self-Check

"What if we removed the labeled break and continue and used only regular break and continue inside the inner loop? How would the time complexity change?"

Practice

1.

What does the break label; statement do in JavaScript?

easy

A. It exits the loop identified by the label immediately.

B. It skips the current iteration of the inner loop only.

C. It restarts the entire program from the beginning.

D. It pauses the loop until a condition is met.

Solution

1. Step 1: Understand labeled break

   The break label; statement exits the loop that has the specified label, not just the innermost loop.

2. Step 2: Compare with normal break

   Normal break exits only the current loop, but labeled break exits the labeled outer loop immediately.

3. Final Answer:

   It exits the loop identified by the label immediately. -> Option A

4. Quick Check:

   break label exits labeled loop [OK]

Hint: Labeled break exits the named loop, not just inner loop [OK]

Common Mistakes:

• Thinking break label only skips current iteration
• Confusing break label with continue label
• Assuming break label pauses the loop

2.

Which of the following is the correct syntax to continue the outer loop labeled outerLoop?

outerLoop: for(let i = 0; i < 3; i++) {
  for(let j = 0; j < 3; j++) {
    // What goes here?
  }
}

easy

A. continue outerLoop;

B. continue (outerLoop);

C. continue: outerLoop;

D. continue to outerLoop;

Solution

1. Step 1: Recall labeled continue syntax

   The correct syntax to continue a labeled loop is continue labelName; without parentheses or extra words.

2. Step 2: Match options with syntax

   continue outerLoop; matches the correct syntax exactly. Options B, C, and D are invalid syntax.

3. Final Answer:

   continue outerLoop; -> Option A

4. Quick Check:

   continue labelName; is correct syntax [OK]

Hint: Use 'continue label;' exactly, no parentheses or colons [OK]

Common Mistakes:

• Adding parentheses around label
• Using colon after continue
• Writing extra words like 'to'

3.

What is the output of the following code?

outer: for(let i = 1; i <= 3; i++) {
  for(let j = 1; j <= 3; j++) {
    if(j === 2) continue outer;
    console.log(i, j);
  }
}

medium

A. 1 1
1 3
2 1
3 1

B. 1 1
2 1
3 1

C. 1 1
1 3
2 1
2 3
3 1
3 3

D. 1 1
2 2
3 3

Solution

1. Step 1: Understand continue outer;

   When j === 2, continue outer; skips to the next iteration of the outer loop, skipping the rest of inner loop and console.log for that i.

2. Step 2: Trace iterations

   For i=1: j=1 logs '1 1', j=2 triggers continue outer (skip to i=2). For i=2: j=1 logs '2 1', j=2 triggers continue outer (skip to i=3). For i=3: j=1 logs '3 1', j=2 triggers continue outer (loop ends after i=3).

3. Final Answer:

   1 1 2 1 3 1 -> Option B

4. Quick Check:

   continue outer skips inner loop rest [OK]

Hint: continue label skips to next outer loop iteration [OK]

Common Mistakes:

• Thinking continue outer skips only inner iteration
• Expecting all inner loop logs
• Confusing break and continue effects

4.

Find the error in this code snippet:

outerLoop: for(let i = 0; i < 2; i++) {
  for(let j = 0; j < 2; j++) {
    if(i === j) break;
    if(j === 1) continue outerLoop;
    console.log(i, j);
  }
}

medium

A. The label name is missing a colon.

B. Using continue outerLoop; inside inner loop is invalid.

C. The break; statement breaks only inner loop, not labeled loop.

D. No error; code runs correctly.

Solution

1. Step 1: Analyze break statement

   The break; without label breaks only the innermost loop, not the labeled outer loop.

2. Step 2: Check labeled continue usage

   The continue outerLoop; is valid and skips to next iteration of the labeled loop.

3. Final Answer:

   The break; statement breaks only inner loop, not labeled loop. -> Option C

4. Quick Check:

   break without label affects inner loop only [OK]

Hint: break without label breaks inner loop only [OK]

Common Mistakes:

• Assuming break breaks labeled loop without label
• Thinking continue outerLoop is invalid
• Confusing label syntax

5.

Given the nested loops below, how can you skip all remaining iterations of the outer loop when j === 3?

outerLoop: for(let i = 1; i <= 5; i++) {
  for(let j = 1; j <= 5; j++) {
    if(j === 3) {
      // What statement here?
    }
    console.log(i, j);
  }
}

hard

A. continue outerLoop;

B. break;

C. continue;

D. break outerLoop;

Solution

1. Step 1: Understand the goal

   We want to stop all remaining iterations of the outer loop when j === 3, meaning exit the outer loop completely.

2. Step 2: Choose correct statement

   break outerLoop; exits the labeled outer loop immediately. Plain break; exits only inner loop. continue; and continue outerLoop; skip iterations but do not exit the outer loop.

3. Final Answer:

   break outerLoop; -> Option D

4. Quick Check:

   break label exits labeled loop [OK]

Hint: Use break label to exit outer loop immediately [OK]

Common Mistakes:

• Using break without label to exit outer loop
• Using continue instead of break
• Confusing continue label with break label