Stack • Applications

Prefix to Postfix Conversion

To convert Prefix to Postfix, we use a String Stack and read backwards. The logic is identical to Prefix-to-Infix, but we don't add parentheses and we put the operator at the end of the combined string.

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The Setup

Read the Prefix string Right-to-Left. Push operands as 1-character strings.

The Assembly

When you hit an operator, pop `val1` then `val2`. Combine them in pure Postfix format: `val1 + val2 + operator`.

No Parentheses

Because we are outputting Postfix, we never add parentheses! The output string remains highly compressed.

*+ab-cd

String Stack

Empty

Code Tracker

:::

1function prefixToPostfix(exp) {

2 let stack = [];

3 for (let i = exp.length - 1; i >= 0; i--) {

4 let char = exp[i];

5 if (isOperand(char)) {

6 stack.push(char);

7 } else {

8 let val1 = stack.pop();

9 let val2 = stack.pop();

10 stack.push(val1 + val2 + char);

11 }

12 }

13 return stack.pop();

14}

Prefix To Postfix

Prefix To Postfix

Prefix to Postfix Conversion

The Setup

The Assembly

No Parentheses

Prefix to Postfix Conversion

The Setup

The Assembly

No Parentheses