Logical operators in Swift - Time & Space Complexity

Time Complexity: Logical operators

O(n)

Understanding Time Complexity

Logical operators combine true or false values to make decisions in code.

We want to see how the time to run code with logical operators changes as input grows.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

func checkConditions(_ values: [Bool]) -> Bool {
    for value in values {
        if value && someOtherCheck() {
            return true
        }
    }
    return false
}

func someOtherCheck() -> Bool {
    return true
}
    

This code checks each Boolean in an array and uses logical AND to decide if it should return true early.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Looping through the array of Booleans.
• How many times: Up to once per element, until a true condition is found.

How Execution Grows With Input

As the array gets bigger, the loop may run more times, but it can stop early if condition is met.

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

Pattern observation: The number of checks grows roughly in direct proportion to input size.

Final Time Complexity

Time Complexity: O(n)

This means the time to run grows linearly with the number of items to check.

Common Mistake

[X] Wrong: "Logical operators always make code run faster, so time complexity is constant."

[OK] Correct: Logical operators themselves are quick, but if used inside loops over many items, total time still grows with input size.

Interview Connect

Understanding how logical operators affect loops helps you explain code efficiency clearly and confidently.

Self-Check

"What if the function someOtherCheck() took longer time to run? How would the time complexity change?"

Practice

1. Which logical operator in Swift returns true only if both conditions are true?

easy

A. == (Equality)

B. || (OR)

C. && (AND)

D. ! (NOT)

Solution

1. Step 1: Understand the AND operator

   The AND operator (&&) returns true only when both conditions it connects are true.

2. Step 2: Compare with other operators

   The OR operator (||) returns true if at least one condition is true, NOT (!) flips true to false and vice versa, and == checks equality, not logical combination.

3. Final Answer:

   && (AND) -> Option C

4. Quick Check:

   AND = && [OK]

Hint: AND needs both true; look for && operator [OK]

Common Mistakes:

• Confusing AND (&&) with OR (||)
• Thinking NOT (!) combines conditions
• Mixing equality (==) with logical operators

2. Which of the following is the correct syntax to negate a Boolean value isActive in Swift?

easy

A. !isActive

B. not isActive

C. isActive!

D. isActive.not()

Solution

1. Step 1: Recall the NOT operator syntax

   In Swift, the NOT operator is written as an exclamation mark (!) placed before the Boolean variable to flip its value.

2. Step 2: Check each option

   !isActive is the correct syntax. The other options are not valid Swift syntax for negation.

3. Final Answer:

   !isActive -> Option A

4. Quick Check:

   NOT = ! before variable [OK]

Hint: Use ! before variable to negate Boolean [OK]

Common Mistakes:

• Writing 'not' instead of '!'
• Putting ! after variable name
• Using method calls like .not()

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

let a = true
let b = false
print(a || b && !b)

medium

A. Syntax Error

B. true

C. false

D. nil

Solution

1. Step 1: Evaluate the NOT operator

   !b means !false which is true.

2. Step 2: Evaluate AND operator

   b && !b is false && true which is false.

3. Step 3: Evaluate OR operator

   a || (result of AND) is true || false which is true.

4. Final Answer:

   true -> Option B

5. Quick Check:

   OR with true = true [OK]

Hint: Remember NOT first, then AND, then OR [OK]

Common Mistakes:

• Ignoring operator precedence
• Evaluating OR before AND
• Misunderstanding ! operator

4. Identify the error in this Swift code snippet:

let x = true
let y = false
if x || && y {
    print("Yes")
}

medium

A. Missing parentheses around conditions

B. print statement syntax error

C. Variables x and y are not Boolean

D. Incorrect use of logical operators together

Solution

1. Step 1: Analyze the if condition syntax

   The condition uses 'x || && y' which combines OR (||) and AND (&&) operators without a proper operand between them.

2. Step 2: Identify the logical operator misuse

   Logical operators must connect two Boolean expressions. Here, '|| &&' is invalid syntax.

3. Final Answer:

   Incorrect use of logical operators together -> Option D

4. Quick Check:

   Operators must connect expressions properly [OK]

Hint: Operators need operands on both sides [OK]

Common Mistakes:

• Writing two operators without a condition between
• Assuming parentheses fix operator misuse
• Confusing variable types with operator errors

5. You want to check if a number n is between 10 and 20 inclusive in Swift. Which condition correctly uses logical operators?

hard

A. n >= 10 && n <= 20

B. n > 10 && n < 20

C. n >= 10 || n <= 20

D. !(n < 10 && n > 20)

Solution

1. Step 1: Understand the range condition

   To check if n is between 10 and 20 inclusive, n must be greater than or equal to 10 AND less than or equal to 20.

2. Step 2: Evaluate each option

   n >= 10 || n <= 20 uses OR which is incorrect because it allows values outside the range. n > 10 && n < 20 excludes 10 and 20 by using > and <. !(n < 10 && n > 20) negates an impossible condition and is incorrect.

3. Final Answer:

   n >= 10 && n <= 20 -> Option A

4. Quick Check:

   Use AND for range checks [OK]

Hint: Use && to combine lower and upper bounds [OK]

Common Mistakes:

• Using OR instead of AND for range
• Excluding boundary values by using > or <
• Using negation incorrectly for range