In this tutorial from RisingBrain, we dive into the classic LeetCode problem Evaluate Reverse Polish Notation (RPN). This problem is a cornerstone for understanding stack-based expression evaluation and is a frequent topic in coding interviews.
The core idea is simple: given an array of tokens representing an arithmetic expression in postfix notation (Reverse Polish Notation), we need to compute the result using a stack. The algorithm processes tokens left to right:
- If the token is an operand (a number), it is pushed onto the stack.
- If the token is an operator (
+,-,*,/), the top two values are popped from the stack, the operation is applied, and the result is pushed back.
For example, the expression ["2","1","+","3","*"] should yield 9 because (2+1)*3 = 9. The stack approach ensures correct evaluation without needing parentheses.
The video includes a detailed dry run of multiple test cases, explaining how the stack changes at each step. This hands-on walkthrough helps solidify understanding.
Code implementations are provided in Java, Python, and C++, making it accessible to a wide audience. You'll also learn edge-case handling, such as division truncation toward zero and handling negative numbers.
By the end of this tutorial, you'll be confident in solving RPN problems and be better prepared for stack-related challenges in interviews.