What is the Evaluate Reverse Polish Notation pattern?

The Evaluate Reverse Polish Notation is a common coding interview pattern in Stack problems. It provides a structured approach to solving related algorithm challenges efficiently.

When should I use Evaluate Reverse Polish Notation?

Use the Evaluate Reverse Polish Notation pattern when you encounter problems matching its characteristics. Check the "When to Use" and "Clues" sections in the lesson for specific indicators.

Is Evaluate Reverse Polish Notation asked in FAANG interviews?

Yes, Evaluate Reverse Polish Notation is an essential pattern commonly tested in FAANG and top tech company technical interviews.

Stack

Medium

Evaluate Reverse Polish Notation

Evaluate the value of an arithmetic expression in Reverse Polish Notation (Postfix).

10 min read

Problem Understanding

You are given an array of strings tokens that represents an arithmetic expression in a Reverse Polish Notation. Evaluate the expression and return an integer.

Valid Operators: +, -, *, /. Integer division truncates toward zero.

Example:

Input: ["2","1","+","3","*"]
Logic: ((2 + 1) * 3) = 9
Output: 9
Input: ["4","13","5","/","+"]
Logic: (4 + (13 / 5)) = 6

Algorithm Strategy

RPN is perfectly suited for a Stack.

Initialize an empty stack.
Iterate through each token.
If token is a number, push it to the stack.
If token is an operator:
- pop the top two elements (say b is top, a is next).
- Perform a <op> b.
- push the result back.
Final result is the only element left in the stack.

Interactive Visualization

Step 1 / 1

Empty Stack

Top Index: -1

Initializing...

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