What Is Prefix Notation in Data Structure?


Angela Bailey

Prefix notation, also known as Polish notation, is a method of writing arithmetic expressions where operators are placed before their operands. In this article, we will explore the concept of prefix notation in data structures and understand its significance in computer science.

Understanding Prefix Notation

In traditional infix notation, we write arithmetic expressions with operators placed between operands. For example, the infix expression “5 + 3” represents the addition of 5 and 3. However, in prefix notation, the same expression would be written as “+ 5 3”.

The main advantage of prefix notation is that it eliminates the need for parentheses to specify the order of operations. Instead, it relies on a fixed position of operators relative to their operands.

How Prefix Notation Works

In prefix notation, each expression starts with an operator followed by its operands. Let’s take a few examples to understand how it works:

  • + 5 3: The “+” operator is applied to the operands 5 and 3, resulting in a sum of 8.
  • * + 4 2 – 6 1: The expression can be evaluated step by step: first add (4 + 2), then subtract (6 -1), and finally multiply the results. It gives us a final result of (6 * 5) =30.

Note that prefix notation allows us to perform complex calculations without using parentheses or worrying about operator precedence. The order of operations is determined solely by the position of operators within the expression.

Implementing Prefix Notation

In data structures and programming languages, prefix notation can be implemented using stacks or recursive algorithms. One common approach is to use a stack to store the operands and evaluate the expression from right to left.

Here’s a simplified algorithm for evaluating prefix expressions:

  1. Create an empty stack.
  2. Read the expression from right to left.
  3. If the token is an operand, push it onto the stack.
  4. If the token is an operator, pop two operands from the stack, apply the operator, and push the result back onto the stack.
  5. Repeat steps 3-4 until all tokens are processed.
  6. The final result will be at the top of the stack.

This algorithm allows us to evaluate prefix expressions efficiently and accurately. It’s widely used in applications that involve complex mathematical calculations such as compilers, calculators, and symbolic algebra systems.


Prefix notation provides a concise and unambiguous way of representing arithmetic expressions. By placing operators before their operands, we can eliminate ambiguity and simplify complex calculations. Understanding prefix notation is essential for anyone working with algorithms, data structures, or mathematical computations in computer science.

So next time you come across a prefix expression, remember that it follows a specific set of rules where operators are positioned before operands. With this knowledge in hand, you’ll be well-equipped to tackle problems involving prefix notation in data structures and beyond!

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