Continue statement with levels in PHP - Time & Space Complexity

Time Complexity: Continue statement with levels

O(n)

Understanding Time Complexity

Let's see how using the continue statement with levels affects how many times parts of the code run.

We want to know how skipping certain loops changes the total work done.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

for ($i = 0; $i < $n; $i++) {
    for ($j = 0; $j < $n; $j++) {
        if ($j % 2 == 0) {
            continue 2; // skips to next $i iteration
        }
        // some constant time operation
    }
}
    

This code loops over two levels. When $j is even, it skips the rest of inner and outer loop body and moves to the next $i.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Nested loops over $i and $j.
• How many times: Outer loop runs $n times; inner loop runs partially due to continue 2.

How Execution Grows With Input

Because continue 2 skips inner and outer loop when $j is even, inner loop does very little work per outer loop.

Input Size (n)	Approx. Operations
10	5 (one inner iteration per outer loop when $j is odd)
100	50
1000	500

Pattern observation: Operations grow roughly linearly with input size, not squared.

Final Time Complexity

Time Complexity: O(n)

This means the total work grows in direct proportion to the input size.

Common Mistake

[X] Wrong: "Since there are two loops, the time must be O(n²)."

[OK] Correct: The continue 2 skips many inner loop steps, so the inner loop does not fully run each time.

Interview Connect

Understanding how control statements like continue with levels affect loops helps you explain code efficiency clearly and confidently.

Self-Check

"What if we changed continue 2 to continue 1? How would the time complexity change?"

Practice

1.

What does the continue statement do inside a loop in PHP?

easy

A. It skips the rest of the current loop iteration and moves to the next iteration.

B. It stops the entire loop immediately.

C. It restarts the whole program.

D. It pauses the loop for a moment.

Solution

1. Step 1: Understand the role of continue in loops

   The continue statement tells the loop to skip the remaining code in the current iteration.

2. Step 2: What happens after continue?

   The loop immediately moves to the next iteration, not stopping the entire loop.

3. Final Answer:

   It skips the rest of the current loop iteration and moves to the next iteration. -> Option A

4. Quick Check:

   continue skips current iteration [OK]

Hint: Remember: continue skips current iteration only [OK]

Common Mistakes:

• Thinking continue stops the whole loop
• Confusing continue with break
• Assuming continue pauses the program

2.

Which of the following is the correct syntax to skip the current iteration of the outer loop in nested loops using continue in PHP?

for ($i = 0; $i < 3; $i++) {
    for ($j = 0; $j < 3; $j++) {
        if ($j == 1) {
            // What continue statement skips outer loop iteration?
        }
    }
}

easy

A. continue 2;

B. continue 1;

C. continue;

D. continue 3;

Solution

1. Step 1: Understand nested loop levels

   There are two loops: outer ($i) and inner ($j). To skip outer loop iteration, we use continue 2;.

2. Step 2: Apply continue n; syntax

   continue 2; skips the current iteration of the second enclosing loop (outer loop).

3. Final Answer:

   continue 2; -> Option A

4. Quick Check:

   continue 2; skips outer loop iteration [OK]

Hint: Use continue n; where n = loop level to skip [OK]

Common Mistakes:

• Using continue without number skips inner loop only
• Using continue 1; which skips inner loop only
• Using continue 3; which is invalid here

3.

What will be the output of the following PHP code?

for ($i = 1; $i <= 3; $i++) {
    for ($j = 1; $j <= 3; $j++) {
        if ($j == 2) {
            continue 2;
        }
        echo "$i$j ";
    }
}

medium

A. 11 13 12 22 32

B. 11 21 31

C. 11 12 13 21 22 23 31 32 33

D. 11 13 21 23 31 33

Solution

1. Step 1: Analyze the nested loops and continue 2;

   When $j == 2, continue 2; skips the rest of the inner and outer loop iteration, moving to next $i.

2. Step 2: Trace output for each iteration

   For $i=1: $j=1 prints '11 ', $j=2 triggers continue 2; skips to $i=2.
   For $i=2: $j=1 prints '21 ', $j=2 triggers continue 2; skips to $i=3.
   For $i=3: $j=1 prints '31 ', $j=2 triggers continue 2; loop ends.

3. Final Answer:

   11 21 31 -> Option B

4. Quick Check:

   continue 2 skips outer loop iteration [OK]

Hint: continue 2 skips outer loop iteration immediately [OK]

Common Mistakes:

• Assuming continue 2 skips only inner loop
• Expecting all combinations printed
• Ignoring that continue 2 skips outer loop iteration

4.

Find the error in this PHP code snippet that tries to skip the outer loop iteration when $j == 2:

for ($i = 0; $i < 3; $i++) {
    for ($j = 0; $j < 3; $j++) {
        if ($j == 2) {
            continue 3;
        }
        echo "$i$j ";
    }
}

medium

A. The continue statement should be break 3; instead.

B. There is no error; the code runs fine.

C. The echo statement is inside the wrong loop.

D. Using continue 3; causes a fatal error because only 2 loops exist.

Solution

1. Step 1: Count the nested loops

   There are only 2 loops: outer ($i) and inner ($j).

2. Step 2: Check the continue level

   continue 3; tries to skip 3 levels, but only 2 exist, causing a fatal error.

3. Final Answer:

   Using continue 3; causes a fatal error because only 2 loops exist. -> Option D

4. Quick Check:

   continue n must not exceed loop depth [OK]

Hint: continue n; must not exceed nested loop count [OK]

Common Mistakes:

• Using continue with number larger than loop depth
• Confusing continue with break
• Ignoring PHP fatal error on invalid continue level

5.

You want to print all pairs (i, j) for i and j from 1 to 3, but skip printing pairs where j == 2 and also skip the entire outer loop iteration if i == 2. Which code snippet correctly uses continue with levels to achieve this?

hard

A. for ($i = 1; $i <= 3; $i++) {
if ($i == 2) continue;
for ($j = 1; $j <= 3; $j++) {
if ($j == 2) continue;
echo "($i,$j) ";
}
}

B. for ($i = 1; $i <= 3; $i++) {
for ($j = 1; $j <= 3; $j++) {
if ($j == 2) continue;
if ($i == 2) continue 2;
echo "($i,$j) ";
}
}

C. for ($i = 1; $i <= 3; $i++) {
for ($j = 1; $j <= 3; $j++) {
if ($i == 2) continue 2;
if ($j == 2) continue;
echo "($i,$j) ";
}
}

D. for ($i = 1; $i <= 3; $i++) {
for ($j = 1; $j <= 3; $j++) {
if ($i == 2 || $j == 2) continue 2;
echo "($i,$j) ";
}
}

Solution

1. Step 1: Understand the requirements

   Skip printing pairs where j == 2, and skip entire outer loop iteration if i == 2.

2. Step 2: Analyze each option

   for ($i = 1; $i <= 3; $i++) {
       if ($i == 2) continue;
       for ($j = 1; $j <= 3; $j++) {
           if ($j == 2) continue;
           echo "($i,$j) ";
       }
   }

   skips i == 2 outer loop correctly but skips j == 2 only in inner loop.
   

   for ($i = 1; $i <= 3; $i++) {
       for ($j = 1; $j <= 3; $j++) {
           if ($j == 2) continue;
           if ($i == 2) continue 2;
           echo "($i,$j) ";
       }
   }

   tries to continue 2 inside inner loop after j check, but order is wrong.
   

   for ($i = 1; $i <= 3; $i++) {
       for ($j = 1; $j <= 3; $j++) {
           if ($i == 2) continue 2;
           if ($j == 2) continue;
           echo "($i,$j) ";
       }
   }

   first skips outer loop iteration if i == 2 using continue 2;, then skips j == 2 in inner loop.
   

   for ($i = 1; $i <= 3; $i++) {
       for ($j = 1; $j <= 3; $j++) {
           if ($i == 2 || $j == 2) continue 2;
           echo "($i,$j) ";
       }
   }

   skips outer loop iteration if either i == 2 or j == 2, which is incorrect.

3. Final Answer:

   Option C correctly uses continue 2; to skip outer loop when i == 2 and continue to skip j == 2. -> Option C

4. Quick Check:

   Use continue 2; to skip outer loop inside inner loop [OK]

Hint: Place continue 2; before continue for inner loop skip [OK]

Common Mistakes:

• Skipping outer loop for wrong conditions
• Using continue 2; incorrectly for inner loop skip
• Combining conditions incorrectly causing wrong skips