Stack • Applications

Postfix to Prefix Conversion

Converting between the two machine notations is simple. The logic is identical to Postfix-to-Infix, except we format the combined string as `operator + val1 + val2` instead of adding parentheses.

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The String Stack

We use the same String Stack approach. Operands are pushed as length-1 strings.

The Assembly

When an operator is encountered, pop `val2` and `val1`. Since we want Prefix notation, the operator must go FIRST. So we concatenate: `operator + val1 + val2`.

No Parentheses

Unlike Infix, Prefix notation does not require parentheses to maintain order of operations, keeping the strings clean and concise.

ab*c+

String Stack

Empty

Code Tracker

:::

1function postfixToPrefix(exp) {

2 let stack = [];

3 for (let char of exp) {

4 if (isOperand(char)) {

5 stack.push(char);

6 } else {

7 let val2 = stack.pop();

8 let val1 = stack.pop();

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

10 }

11 }

12 return stack.pop();

13}

Postfix To Prefix

Postfix To Prefix

Postfix to Prefix Conversion

The String Stack

The Assembly

No Parentheses

Postfix to Prefix Conversion

The String Stack

The Assembly

No Parentheses