Basic Calculator II
mediumTime: O(n)Space: O(n)
Signals to notice
evaluate +, -, ×, ÷ without parenthesesoperator precedencestack for deferred addition
Brute force first
Not applicable — parsing requires precedence handling.
The key insight
Stack: for + and -, push number (with sign). For × and ÷, pop top, compute, push result. Sum stack at end. O(n).
What must stay true
× and ÷ resolve immediately (high precedence). + and - are deferred (pushed). Final sum = the answer.
Easy way to go wrong
Integer division toward zero — use Math.trunc(), not Math.floor().