Basic Calculator
A hard-tier problem at 46% community acceptance, tagged with Math, String, Stack. Reported in interviews at Rokt and 16 others.
Basic Calculator shows up hard on the difficulty scale but lands in about 46% of submissions, which means most people either nail it or crater. Amazon, ByteDance, Tesla, and Snowflake have all asked it. The trick isn't complexity; it's state management. You're parsing a string with +, -, *, / and whitespace, respecting operator precedence, and you can't just build an expression tree on the fly. Most candidates try to evaluate left-to-right and fail on something like '2-3*4'. If this problem hits your live assessment and you blank on the precedence trap, StealthCoder solves it in seconds, invisible to the proctor.
Companies that ask "Basic Calculator"
Basic Calculator is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Made for the engineer who has done the work but might still blank with a webcam pointed at him.
Get StealthCoderThe core pattern is a single-pass stack. You iterate through the string, accumulate digits, and when you hit an operator (or reach the end), you apply the previous operator to the current number. Multiplication and division happen immediately; addition and subtraction get pushed to the stack for later. Whitespace is a noise filter. The common failure is trying to parse and evaluate simultaneously without tracking the last operator, or building intermediate results that don't respect order of operations. Once you see the stack approach, it's straightforward: iterate, maintain state for the last operator and current number, handle each operator correctly, sum the stack at the end. StealthCoder is the hedge if you've drilled recursion and string problems but haven't internalized this specific stack rhythm.
Pattern tags
You know the problem.
Make sure you actually pass it.
Basic Calculator recycles across companies for a reason. It's hard-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Made for the engineer who has done the work but might still blank with a webcam pointed at him. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Basic Calculator interview FAQ
Is Basic Calculator really asked by big companies like Amazon and Tesla?+
Yes. It appears across 17 companies in the reports, including Amazon, ByteDance, Tesla, Snowflake, and DoorDash. Hard label means it screens strong technical candidates. It's not a trick question; it's a signal test for careful state management and parsing.
What's the trick that makes 46% of people fail?+
Operator precedence. A naive left-to-right evaluation breaks on '2-3*4'. The stack lets you defer addition and subtraction while executing *, / immediately. Most failures come from parsing correctly but evaluating wrong.
Do I need recursion or is stack iteration enough?+
Stack iteration is the standard and cleanest path. Recursion can work for nested parentheses if the problem extends that far, but Basic Calculator (without parentheses in the base version) is solved efficiently with a single loop and a stack.
How do I handle whitespace without breaking the parse?+
Skip it. Whitespace doesn't affect state transitions. When iterating, check 'if character is space, continue'. Don't let it reset your current number accumulator or trigger premature operator application.
Is this problem still asked or is it outdated?+
Still current. It appears across Rokt, Ripple, Snowflake, Amazon, ByteDance, Tesla, and others. The acceptance rate holds steady around 46%, suggesting it remains a live screening tool for parsing and state-management skill.
Want the actual problem statement? View "Basic Calculator" on LeetCode →