Stack • Applications

Prefix to Infix Conversion

Converting Prefix back to Infix requires reading the string backwards and wrapping elements in parentheses as they are joined.

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Backwards Scan

Because Prefix notation puts the operator before the operands, we must scan from Right to Left to hit the operands first.

Pop Order

Because we are scanning backwards, the FIRST popped element is `val1` (the left operand) and the SECOND popped element is `val2` (the right operand).

The String Stack

As always, the stack stores intermediate string chunks wrapped in `()`. When the loop finishes, the one remaining string is the full Infix expression.

*+ab-cd

String Stack

Empty

Code Tracker

:::

1function prefixToInfix(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 + char + val2 + ')');

11 }

12 }

13 return stack.pop();

14}

Prefix To Infix

Prefix To Infix

Prefix to Infix Conversion

Backwards Scan

Pop Order

The String Stack

Prefix to Infix Conversion

Backwards Scan

Pop Order

The String Stack