Switch-case statements in MATLAB - Time & Space Complexity

Time Complexity: Switch-case statements

O(n)

Understanding Time Complexity

We want to understand how the time it takes to run a switch-case statement changes as the number of cases grows.

Specifically, how does checking each case affect the total work done?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

switch value
    case 1
        disp('One');
    case 2
        disp('Two');
    case 3
        disp('Three');
    otherwise
        disp('Other');
end
    

This code checks the variable value against several cases and runs the matching block.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Checking each case one by one until a match is found.
• How many times: Up to the number of cases in the switch statement.

How Execution Grows With Input

As the number of cases increases, the program may need to check more cases before finding a match.

Input Size (number of cases)	Approx. Operations (case checks)
10	Up to 10 checks
100	Up to 100 checks
1000	Up to 1000 checks

Pattern observation: The number of checks grows directly with the number of cases.

Final Time Complexity

Time Complexity: O(n)

This means the time to find the matching case grows linearly with the number of cases.

Common Mistake

[X] Wrong: "Switch-case statements always run in constant time because they just jump to the right case."

[OK] Correct: Actually, the program may check cases one by one until it finds a match, so time grows with the number of cases.

Interview Connect

Understanding how switch-case statements scale helps you explain code efficiency clearly and shows you can think about how programs behave as they grow.

Self-Check

"What if the switch-case was replaced by a hash map lookup? How would the time complexity change?"

Practice

1. What is the main purpose of a switch-case statement in MATLAB?

easy

A. To repeat a block of code multiple times

B. To create a new variable

C. To define a function

D. To execute different blocks of code based on the value of a variable

Solution

1. Step 1: Understand the role of switch-case

   A switch-case statement chooses which code to run depending on a variable's value.

2. Step 2: Compare with other options

   Repeating code is done by loops, defining functions is different, and creating variables is unrelated.

3. Final Answer:

   To execute different blocks of code based on the value of a variable -> Option D

4. Quick Check:

   Switch-case selects code by value [OK]

Hint: Switch-case runs code based on one variable's value [OK]

Common Mistakes:

• Confusing switch-case with loops
• Thinking switch-case defines functions
• Assuming switch-case creates variables

2. Which of the following is the correct syntax to start a switch-case block in MATLAB?

easy

A. switch variable

B. case variable

C. switch-case(variable)

D. switch = variable

Solution

1. Step 1: Recall switch-case syntax

   The switch statement starts with the keyword switch followed by the variable name.

2. Step 2: Check each option

   switch variable matches correct syntax. Options A, B, and C are invalid MATLAB syntax for switch.

3. Final Answer:

   switch variable -> Option A

4. Quick Check:

   Start switch with 'switch variable' [OK]

Hint: Start switch with 'switch' plus variable name [OK]

Common Mistakes:

• Using parentheses after switch
• Writing 'case' instead of 'switch' to start
• Assigning variable with '=' in switch

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

color = 'green';
switch color
    case 'red'
        disp('Stop')
    case 'green'
        disp('Go')
    otherwise
        disp('Wait')
end

medium

A. Go

B. Wait

C. Stop

D. Error

Solution

1. Step 1: Check the value of variable 'color'

   The variable color is set to 'green'.

2. Step 2: Match the case in switch

   The switch checks cases: 'red' (no), 'green' (yes), so it runs disp('Go').

3. Final Answer:

   Go -> Option A

4. Quick Check:

   color='green' triggers 'Go' [OK]

Hint: Match variable value to case labels to find output [OK]

Common Mistakes:

• Choosing output from wrong case
• Ignoring the otherwise block
• Assuming syntax error

4. Identify the error in this MATLAB switch-case code:

value = 10;
switch value
case 5
    disp('Five')
case 10
    disp('Ten')
case
    disp('Other')
end

medium

A. Incorrect variable name in switch

B. Missing 'otherwise' keyword for default case

C. Missing 'end' statement

D. Case values must be strings

Solution

1. Step 1: Review the case statements

   The last case has no value and no keyword 'otherwise'. MATLAB requires 'otherwise' for default.

2. Step 2: Check syntax rules

   Case values can be numbers, 'end' is present, variable name is correct.

3. Final Answer:

   Missing 'otherwise' keyword for default case -> Option B

4. Quick Check:

   Default case needs 'otherwise' keyword [OK]

Hint: Use 'otherwise' for default case, not empty case [OK]

Common Mistakes:

• Leaving case without value or otherwise
• Thinking 'end' is missing
• Believing case values must be strings

5. You want to write a MATLAB switch-case that prints 'Weekend' for days 'Saturday' and 'Sunday', 'Weekday' for Monday to Friday, and 'Invalid' otherwise. Which code correctly implements this?

hard

A. switch day
case ['Saturday', 'Sunday']
disp('Weekend')
case ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday']
disp('Weekday')
otherwise
disp('Invalid')
end

B. switch day
case 'Saturday' || 'Sunday'
disp('Weekend')
case 'Monday' || 'Tuesday' || 'Wednesday' || 'Thursday' || 'Friday'
disp('Weekday')
otherwise
disp('Invalid')
end

C. switch day
case {'Saturday', 'Sunday'}
disp('Weekend')
case {'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday'}
disp('Weekday')
otherwise
disp('Invalid')
end

D. switch day
case 'Saturday', 'Sunday'
disp('Weekend')
case 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday'
disp('Weekday')
otherwise
disp('Invalid')
end

Solution

1. Step 1: Understand how to group cases in MATLAB

   MATLAB allows grouping multiple values in a cell array inside case, like {'Saturday', 'Sunday'}.

2. Step 2: Check each option's syntax

   switch day case {'Saturday', 'Sunday'} disp('Weekend') case {'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday'} disp('Weekday') otherwise disp('Invalid') end uses correct cell arrays for grouping. switch day case 'Saturday' || 'Sunday' disp('Weekend') case 'Monday' || 'Tuesday' || 'Wednesday' || 'Thursday' || 'Friday' disp('Weekday') otherwise disp('Invalid') end uses invalid '||' inside case. switch day case ['Saturday', 'Sunday'] disp('Weekend') case ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday'] disp('Weekday') otherwise disp('Invalid') end uses square brackets which is wrong for strings. switch day case 'Saturday', 'Sunday' disp('Weekend') case 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday' disp('Weekday') otherwise disp('Invalid') end uses commas incorrectly.

3. Final Answer:

   Code with cell arrays for grouped cases -> Option C

4. Quick Check:

   Group cases with cell arrays {} in switch-case [OK]

Hint: Group multiple cases using curly braces {} [OK]

Common Mistakes:

• Using || inside case labels
• Using square brackets for string groups
• Separating cases with commas instead of cell arrays