Heterogeneous enums in Typescript - Time & Space Complexity

Time Complexity: Heterogeneous enums

O(n)

Understanding Time Complexity

We want to understand how the time needed to use heterogeneous enums changes as the enum size grows.

Specifically, how does accessing or searching enum values behave when enums mix strings and numbers?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

    enum MixedEnum {
      No = 0,
      Yes = 1,
      Maybe = 2,
      Later = "later"
    }

    function isValueInEnum(value: string | number): boolean {
      return Object.values(MixedEnum).includes(value);
    }
    

This code defines a heterogeneous enum with both numbers and strings, then checks if a value exists in it.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The call to Object.values(MixedEnum) creates an array of enum values, then includes checks each element one by one.
• How many times: The includes method may check up to all enum values, so it runs once per enum value.

How Execution Grows With Input

As the enum gets bigger, the number of checks grows directly with the number of enum values.

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

Pattern observation: The time grows in a straight line with the number of enum values.

Final Time Complexity

Time Complexity: O(n)

This means the time to check a value grows directly with the number of enum entries.

Common Mistake

[X] Wrong: "Checking if a value is in an enum is always instant, no matter the size."

[OK] Correct: Because includes checks each value one by one, bigger enums take longer to search.

Interview Connect

Understanding how enum lookups scale helps you write efficient code and explain your reasoning clearly in interviews.

Self-Check

What if we stored enum values in a Set instead of an array? How would the time complexity change?

Practice

1.

What is a heterogeneous enum in TypeScript?

easy

A. An enum that contains both string and numeric values.

B. An enum that only contains numeric values.

C. An enum that only contains string values.

D. An enum that cannot be used with functions.

Solution

1. Step 1: Understand enum value types

   Enums in TypeScript can hold numeric or string values.

2. Step 2: Define heterogeneous enum

   A heterogeneous enum mixes both string and numeric values in the same enum.

3. Final Answer:

   An enum that contains both string and numeric values. -> Option A

4. Quick Check:

   Heterogeneous enum = mixed string and number values [OK]

Hint: Remember: mixed types in one enum means heterogeneous [OK]

Common Mistakes:

• Thinking enums can only have one type of value
• Confusing heterogeneous with union types
• Assuming enums can't mix strings and numbers

2.

Which of the following is the correct syntax to declare a heterogeneous enum?

enum Status {
  Active = 1,
  Inactive = "NO"
}

easy

A. Incorrect because enum members must be all strings.

B. Incorrect because enums cannot have string values.

C. Incorrect because enum members must be all numbers.

D. Correct syntax with mixed number and string values.

Solution

1. Step 1: Check enum member types

   The enum has one numeric value (1) and one string value ("NO").

2. Step 2: Validate TypeScript enum rules

   TypeScript allows heterogeneous enums mixing numbers and strings.

3. Final Answer:

   Correct syntax with mixed number and string values. -> Option D

4. Quick Check:

   Mixed values in enum = valid heterogeneous enum [OK]

Hint: Look for mixed number and string values in enum members [OK]

Common Mistakes:

• Assuming enums can't have string values
• Thinking all enum members must be same type
• Confusing enum syntax with object literals

3.

What will be the output of the following TypeScript code?

enum Mixed {
  Yes = 1,
  No = "NO"
}
console.log(Mixed.Yes);
console.log(Mixed.No);
console.log(Mixed[1]);

medium

A. Yes, NO, 1

B. 1, NO, Yes

C. 1, NO, undefined

D. NO, 1, Yes

Solution

1. Step 1: Check enum values

   Mixed.Yes is 1, Mixed.No is "NO".

2. Step 2: Understand reverse mapping

   Numeric enums have reverse mapping, so Mixed[1] returns "Yes".

3. Final Answer:

   1, NO, Yes -> Option B

4. Quick Check:

   Numeric enum reverse lookup works, string does not [OK]

Hint: Only numeric enum members have reverse mapping [OK]

Common Mistakes:

• Expecting string enum members to have reverse mapping
• Confusing enum member names with values
• Assuming Mixed[1] returns 1

4.

Identify the error in this heterogeneous enum declaration:

enum Colors {
  Red = "RED",
  Green,
  Blue = 3
}

medium

A. Enums cannot mix string and number values.

B. Blue cannot be assigned a number after a string member.

C. Green must have an explicit string or number value.

D. Red cannot be assigned a string value.

Solution

1. Step 1: Check enum member values

   Red is assigned a string "RED". Green has no value assigned.

2. Step 2: Understand enum auto-increment rules

   After a string member, numeric auto-increment is not allowed. Green must have explicit value.

3. Final Answer:

   Green must have an explicit string or number value. -> Option C

4. Quick Check:

   Members after string need explicit values [OK]

Hint: After string enum member, next must have explicit value [OK]

Common Mistakes:

• Assuming auto-increment works after string member
• Thinking enums can't mix types at all
• Ignoring missing value for Green

5.

You want to create a heterogeneous enum to represent user roles with numeric IDs and string labels. Which enum declaration correctly achieves this?

enum UserRole {
  Admin = 1,
  Guest = "GUEST",
  Member = 2
}

hard

A. This enum is valid and mixes numbers and strings correctly.

B. This enum is invalid because Guest must be a number.

C. This enum is invalid because Admin and Member must be strings.

D. This enum is invalid because Member cannot be a number after a string.

Solution

1. Step 1: Analyze enum member assignments

   Admin=1 (number), Guest="GUEST" (string), Member=2 (number). All explicitly assigned.

2. Step 2: Validate heterogeneous enum rules

   TypeScript allows explicit mixing of numeric and string values in enums.

3. Final Answer:

   This enum is valid and mixes numbers and strings correctly. -> Option A

4. Quick Check:

   Explicit assignments allow mixing numbers after strings [OK]

Hint: Explicit numeric assignments work after string members [OK]

Common Mistakes:

• Thinking numbers cannot follow strings even explicitly
• Confusing explicit assignments with auto-increment rules
• Assuming strict ordering prevents mixing