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Learn Data Structures and Algorithms in JavaScript

Problem: Evaluate Reverse Polish Notation

Understand how to evaluate arithmetic expressions in Reverse Polish Notation by using a stack data structure. Learn to process tokens representing operands and operators, apply operations in the correct order, and implement an efficient solution in JavaScript. This lesson helps you master RPN evaluation along with its time and space complexity analysis.

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Statement

You are given an array of strings tokens representing a valid arithmetic expression in Reverse Polish Notation (RPN). Your task is to evaluate the expression and return an integer representing the value of the expression.

Note: The valid operators are '+', '-', '*', and '/'.
Each operand may be an integer or another expression.
Division between two integers always truncates toward zero.
There will not be any division by zero.
The input is guaranteed to represent a valid arithmetic expression in Reverse Polish Notation.
The answer and all intermediate calculations can be represented in a 3232‑bit integer.

Constraints:

  • 1≤1 \leq tokens.length ≤104\leq 10^4

  • tokens[i] is either an operator: "+", "-" ...