Evaluate arithmetic expression with variables

Q: Evaluate arithmetic expression with variables

This question evaluates implementation skills for a linear-time expression parser and evaluator, covering tokenization, variable substitution, operator precedence and associativity (including unary +/−), parentheses handling, integer arithmetic semantics (division truncation), error detection, and adherence to O(L) time and space constraints.

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Question

Implement an expression evaluator for a string expr containing non-negative integers, variables (alphabetic names), operators +, -, , /, parentheses '()' and spaces. Given a dictionary mapping variable names to integer values, compute the signed 64-bit result using standard operator precedence (/ before +-), left-to-right associativity, and support unary +/-. Division truncates toward zero. The evaluator must run in O(L) time where L is the length of expr and use O(L) extra space. Return an error for invalid tokens or mismatched parentheses. Follow-ups: extend to exponentiation '^' (right-associative) and a function max(a,b).

Evaluate arithmetic expression with variables

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