Nested conditional statements in Javascript - Time & Space Complexity

Time Complexity: Nested conditional statements

O(1)

Understanding Time Complexity

We want to see how the time it takes to run nested conditional statements changes as input changes.

Specifically, we ask: does adding more conditions make the program slower as inputs grow?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

function checkNumber(num) {
  if (num > 0) {
    if (num % 2 === 0) {
      return 'Positive even';
    } else {
      return 'Positive odd';
    }
  } else {
    return 'Non-positive';
  }
}
    

This code checks if a number is positive and then if it is even or odd.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: There are no loops or repeated steps; only simple checks.
• How many times: Each condition runs once per function call.

How Execution Grows With Input

The time to run this code does not increase when the input number gets bigger.

Input Size (n)	Approx. Operations
10	3 checks
100	3 checks
1000	3 checks

Pattern observation: The number of steps stays the same no matter the input size.

Final Time Complexity

Time Complexity: O(1)

This means the time to run the code stays constant no matter how big the input is.

Common Mistake

[X] Wrong: "More conditions always make the program slower as input grows."

[OK] Correct: Nested conditions run only once per input, so they do not slow down with bigger inputs.

Interview Connect

Understanding that nested conditions do not add time with bigger inputs helps you explain code efficiency clearly and confidently.

Self-Check

"What if we added a loop inside the nested conditions? How would the time complexity change?"

Practice

1. What does a nested conditional statement mean in JavaScript?
if (condition1) { if (condition2) { /* code */ } }

easy

A. A loop inside a condition

B. A condition inside another condition

C. Two conditions checked at the same time

D. A function inside a condition

Solution

1. Step 1: Understand the structure of nested conditionals

   Nested conditionals mean one if statement is placed inside another if statement's block.

2. Step 2: Identify the meaning of the code snippet

   The code checks condition1 first, and only if true, it checks condition2 inside it.

3. Final Answer:

   A condition inside another condition -> Option B

4. Quick Check:

   Nested conditional = condition inside condition [OK]

Hint: Look for if inside another if block [OK]

Common Mistakes:

• Thinking nested means conditions checked together
• Confusing nested conditionals with loops
• Assuming functions are involved

2. Which of the following is the correct syntax for nested if statements in JavaScript?

easy

A. if (a > 0) { if (b > 0) { console.log('Both positive'); } }

B. if (a > 0) if (b > 0) console.log('Both positive'); }

C. if (a > 0) { if (b > 0) console.log('Both positive'); } else }

D. if a > 0 { if b > 0 { console.log('Both positive'); } }

Solution

1. Step 1: Check proper use of braces and parentheses

   if (a > 0) { if (b > 0) { console.log('Both positive'); } } uses parentheses for conditions and braces to group code blocks correctly.

2. Step 2: Verify syntax correctness

   The other options have missing or misplaced braces or parentheses causing syntax errors.

3. Final Answer:

   if (a > 0) { if (b > 0) { console.log('Both positive'); } } -> Option A

4. Quick Check:

   Correct nested if syntax = if (a > 0) { if (b > 0) { console.log('Both positive'); } } [OK]

Hint: Match each if with parentheses and braces [OK]

Common Mistakes:

• Missing braces for inner if block
• Omitting parentheses around conditions
• Extra or misplaced braces

3. What will be the output of this code?

let x = 5;
if (x > 0) {
  if (x < 10) {
    console.log('A');
  } else {
    console.log('B');
  }
} else {
  console.log('C');
}

medium

A. No output

B. B

C. C

D. A

Solution

1. Step 1: Evaluate the outer if condition

   x = 5, which is greater than 0, so the outer if block runs.

2. Step 2: Evaluate the inner if condition

   Inside, x < 10 is true (5 < 10), so it prints 'A'.

3. Final Answer:

   A -> Option D

4. Quick Check:

   5 > 0 and 5 < 10 prints 'A' [OK]

Hint: Check outer condition first, then inner [OK]

Common Mistakes:

• Ignoring inner else block
• Confusing output with 'B' or 'C'
• Assuming no output if conditions are true

4. Find the error in this nested conditional code:

let num = 10;
if (num > 5) {
  if num < 15 {
    console.log('Inside range');
  }
}

medium

A. Using console.log incorrectly

B. Missing braces for outer if block

C. Missing parentheses around inner if condition

D. No error, code is correct

Solution

1. Step 1: Check syntax of inner if statement

   Inner if is written as if num < 15 { missing parentheses around condition.

2. Step 2: Confirm correct syntax for if statements

   JavaScript requires parentheses around conditions: if (num < 15) {.

3. Final Answer:

   Missing parentheses around inner if condition -> Option C

4. Quick Check:

   if conditions need parentheses [OK]

Hint: Always put parentheses around if conditions [OK]

Common Mistakes:

• Forgetting parentheses in if conditions
• Assuming braces are optional
• Thinking console.log causes error

5. You want to write a nested conditional that prints:
- 'Small positive' if a number is > 0 and < 10
- 'Large positive' if a number is >= 10
- 'Non-positive' otherwise
Which code correctly implements this?

hard

A. if (num > 0) { if (num < 10) { console.log('Small positive'); } else { console.log('Large positive'); } } else { console.log('Non-positive'); }

B. if (num > 0 && num < 10) { console.log('Small positive'); } else if (num >= 10) { console.log('Large positive'); } else { console.log('Non-positive'); }

C. if (num > 0) { if (num <= 10) { console.log('Small positive'); } else { console.log('Large positive'); } } else { console.log('Non-positive'); }

D. if (num >= 0) { if (num < 10) { console.log('Small positive'); } else { console.log('Large positive'); } } else { console.log('Non-positive'); }

Solution

1. Step 1: Check conditions for small positive numbers

   if (num > 0) { if (num < 10) { console.log('Small positive'); } else { console.log('Large positive'); } } else { console.log('Non-positive'); } checks if num > 0, then inside if num < 10 to print 'Small positive'.

2. Step 2: Check conditions for large positive and non-positive

   Else inside outer if prints 'Large positive' for num >= 10, else prints 'Non-positive'.

3. Step 3: Verify other options

   The option with combined conditions (&& and else if) is logically correct but does not use nested if statements. The option with outer condition num >= 0 incorrectly classifies 0 as 'Small positive'. The option with inner condition num <= 10 incorrectly classifies 10 as 'Small positive'.

4. Final Answer:

   if (num > 0) { if (num < 10) { console.log('Small positive'); } else { console.log('Large positive'); } } else { console.log('Non-positive'); } -> Option A

5. Quick Check:

   Nested if with correct ranges = if (num > 0) { if (num < 10) { console.log('Small positive'); } else { console.log('Large positive'); } } else { console.log('Non-positive'); } [OK]

Hint: Check each condition range carefully in nested ifs [OK]

Common Mistakes:

• Using <= instead of < for small positive
• Including zero as positive
• Not nesting conditions properly