Basic Calculator

HardStackMonotonic Stack

Solve this the way you would in the interview: out loud, on a timer, with an AI interviewer asking follow-ups while you code. You get a scored report at the end.

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Problem

Given a string s representing a valid expression, implement a basic calculator to evaluate it, and return the result of the evaluation. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions, such as eval(). The expression may contain non-negative integers, +, -, (, ), and spaces.

Examples

Input: s = "1 + 1"
Output: 2
Input: s = " 2-1 + 2 "
Output: 3
Input: s = "(1+(4+5+2)-3)+(6+8)"
Output: 23

Constraints

  • 1 <= s.length <= 3 * 10^5
  • s consists of digits, '+', '-', '(', ')', and ' '.
  • s represents a valid expression.
  • The answer is guaranteed to fit in a 32-bit integer.

What the interviewer grades

A correct solution is one of five scores. The report also grades problem understanding (did you clarify inputs and edge cases before coding), problem solving, communication while you work, code quality, and testing. See a sample report, or read up on the pattern in the lessons.

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