Final Value of Variable After Performing Operations

Final Value of Variable After Performing Operations

What is this problem about?

The Final Value of Variable interview question is a basic simulation problem. You start with a variable X initialized to 0. You are given an array of strings representing operations: "++X", "X++", "--X", and "X--". The operations with ++ increment X by 1, and the operations with -- decrement X by 1. Your task is to return the final value of X.

Why is this asked in interviews?

Companies like Meta and Bloomberg use this simulation interview pattern as a warm-up question or for entry-level screening. it tests your ability to parse strings and implement a simple state machine. It evaluates basic coding hygiene, such as handling loops and string comparisons cleanly.

Algorithmic pattern used

This is a simple Linear Scan / Simulation.

1. Initialize X = 0.
2. Iterate through every string op in the array.
3. Check the operation type:
   • If the string contains +, increment X.
   • If the string contains -, decrement X.
4. Note: You only need to check the second character of each string (e.g., op[1]) to determine if it's an increment or decrement.

Example explanation

Operations: ["--X", "X++", "X++"]

1. X = 0.
2. "--X": Decrement X. X = -1.
3. "X++": Increment X. X = 0.
4. "X++": Increment X. X = 1. Final result: 1.

Common mistakes candidates make

• Complex parsing: Using regex or complex string splitting when a simple if "+" in op or checking op[1] is sufficient.
• Case Sensitivity: While not usually an issue here, not verifying if "x++" (lowercase) is possible.
• Wrong starting value: Initializing X to something other than 0.

Interview preparation tip

In simple string problems, look for the most efficient way to distinguish between cases. For example, in this problem, the character at index 1 is always the operator (+ or -), regardless of whether it's a prefix or postfix operation.