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Infix postfix prefix

 import java.util.Stack;

import java.util.Scanner;

public class ExpressionConverter {

    // Function to return precedence of operators

    static int precedence(char ch) {

        switch (ch) {

            case '+':

            case '-':

                return 1;

            case '*':

            case '/':

                return 2;

            case '^':

                return 3;

        }

        return -1; // For non-operators

    }

    // Function to convert infix to postfix

    static String infixToPostfix(String expression) {

        StringBuilder result = new StringBuilder();

        Stack<Character> stack = new Stack<>();

        for (int i = 0; i < expression.length(); i++) {

            char c = expression.charAt(i);

            // If the character is an operand, add it to the output

            if (Character.isLetterOrDigit(c)) {

                result.append(c);

            }

            // If the character is '(', push it to stack

            else if (c == '(') {

                stack.push(c);

            }

            // If the character is ')', pop from stack to output until '(' is encountered

            else if (c == ')') {

                while (!stack.isEmpty() && stack.peek() != '(') {

                    result.append(stack.pop());

                }

                if (!stack.isEmpty() && stack.peek() == '(') {

                    stack.pop(); // Discard the '('

                }

            }

            // If an operator is encountered

            else {

                // Pop operators with higher or equal precedence from the stack

                while (!stack.isEmpty() && precedence(c) <= precedence(stack.peek())) {

                    result.append(stack.pop());

                }

                stack.push(c);

            }

        }

        // Pop all the remaining operators from the stack

        while (!stack.isEmpty()) {

            result.append(stack.pop());

        }

        return result.toString();

    }

    

    // Function to convert infix to prefix

    static String infixToPrefix(String expression) {

        // The algorithm for infix to prefix is:

        // 1. Reverse the infix expression.

        // 2. Swap '(' and ')' in the reversed expression.

        // 3. Convert the modified expression to postfix.

        // 4. Reverse the resulting postfix expression to get the prefix expression.

        StringBuilder reversedInfix = new StringBuilder(expression).reverse();

        for (int i = 0; i < reversedInfix.length(); i++) {

            char c = reversedInfix.charAt(i);

            if (c == '(') {

                reversedInfix.setCharAt(i, ')');

            } else if (c == ')') {

                reversedInfix.setCharAt(i, '(');

            }

        }

        // Convert the modified string to postfix

        String postfixForReversed = infixToPostfix(reversedInfix.toString());

        // Reverse the result to get prefix

        return new StringBuilder(postfixForReversed).reverse().toString();

    }

    // Main method to test the conversion

    public static void main(String[] args) {

        Scanner scanner = new Scanner(System.in);

        System.out.println("Enter an infix expression (use single letters/digits and operators, no spaces, e.g., a+b*c): ");

        String infixExpression = scanner.nextLine();

        String postfix = infixToPostfix(infixExpression);

        String prefix = infixToPrefix(infixExpression);

        System.out.println("Infix Expression: " + infixExpression);

        System.out.println("Postfix Expression: " + postfix);

        System.out.println("Prefix Expression: " + prefix);

    }

}