What is the optimal time complexity of solving Evaluate Reverse Polish Notation?

The optimized solution achieves a time complexity of O(n) by using sorting, mathematical shortcuts, or hash table lookups.

What is the auxiliary space complexity for Evaluate Reverse Polish Notation?

The space complexity is O(1) since we only use a minimal/constant amount of extra memory for tracking variables (or auxiliary space if dynamic structures are allocated).

What are the typical edge cases we must handle in Evaluate Reverse Polish Notation?

Key edge cases include empty collections, negative or large bounds causing integer overflow, arrays with only one element, or inputs where target criteria are not met.

How can we optimize the brute force approach for Evaluate Reverse Polish Notation?

Brute force methods often inspect all possible combinations. We optimize this by sorting the input list to enable binary search, or tracking processed items in a set to avoid redundant nested loop lookups.

Back to Practice Dashboard

Top 150 InterviewEasy

Evaluate Reverse Polish Notation

Learn how to solve the 'Evaluate Reverse Polish Notation' problem. This detailed resource details brute force and optimized approaches.

Mode Selected

Problem Statement

Easy

You are given an array of strings tokens that represents an arithmetic expression in Reverse Polish Notation.

Evaluate the expression and return an integer that represents the value of the expression.

Note that:

- The valid operators are '+', '-', '*', and '/'.

- Each operand may be an integer or another expression.

- The division between two integers always truncates toward zero.

- There will not be any division by zero.

- The input represents a valid arithmetic expression in reverse polish notation.

Write a function evalRPN(tokens: List[str]) -> int.

Constraints

•1 <= len(tokens) <= 10^4
•tokens[i] is either an operator (+, -, *, /) or an integer in the range [-200, 200]

Examples

Example 1

Input

tokens = ["2", "1", "+", "3", "*"]

Output

Explanation

((2 + 1) * 3) = 9.

Example 2

Input

tokens = ["4", "13", "5", "/", "+"]

Output

Explanation

(4 + (13 / 5)) = (4 + 2) = 6. Note 13/5 truncates to 2.

Example 3

Input

tokens = ["10", "6", "9", "3", "+", "-11", "*", "/", "*", "17", "+", "5", "+"]

Output

Explanation

((10 * (6 / ((9 + 3) * -11))) + 17 + 5) = 22.

Need a Hint?

Analyze the input constraints. Try sorting first (O(n log n)) or using a hash map/set to track seen elements in O(n) time.

Edge Cases to Watch

Empty list or null input variables
Single item lists/arrays
Extremely large input bounds causing integer or stack overflow

Ready to Solve?

Open the problem in PyRun's browser-based Python editor. Your code runs fully offline — no server required.

Open in Editor