Overview

This is a sample program that converts mathematical expressions to Reverse Polish Notation. Algorithm source: http://www.gg.e-mansion.com/~kkatoh/program/novel2/novel208.html Formula source: http://www.wdic.org/w/SCI/%E9%80%86%E3%83%9D%E3%83%BC%E3%83%A9%E3%83%B3%E3%83%89%E8%A8%98%E6%B3%95

Thank you

Details

It's just converted to Polish notation based on the formula. I'm just making the algorithm in Java, so I'm grateful to the quoter.

`Rpn.java`


/**
 *Algorithm quote: http://www.gg.e-mansion.com/~kkatoh/program/novel2/novel208.html
 */
public class Rpn {
    public static void main(String[] args) {
        //Expression quote: http://www.wdic.org/w/SCI/%E9%80%86%E3%83%9D%E3%83%BC%E3%83%A9%E3%83%B3%E3%83%89%E8%A8%98%E6%B3%95
        String formula = "a+b"; // ab+
//        String formula = "a+(b*c)"; // abc*+
//        String formula = "(a+b)*c"; // ab+c*
//        String formula = "a*b+c*d+e*f"; // ab*cd*ef*++
//        String formula = "((a+b)*(c+d)+e)*f"; // ab+cd+*e+f*

        System.out.println(getRpn(formula));
    }

    /**
     *Convert formulas to reverse Polish notation.
     *
     * @param formula Reverse Polish notation Formula to be converted
     * @return Formula converted to reverse Polish notation
     */
    public static String getRpn(String formula) {
        char[] sequenceList  = formula.toCharArray();
        //StringBuilder to store the return value
        StringBuilder resultBuilder = new StringBuilder(sequenceList.length);
        Deque<Character> stack = new ArrayDeque<>();

        //Continue looping until you convert all formulas to Reverse Polish Notation
        for(char token : sequenceList){
            switch (token) {
                case '+':
                case '-':
                    //If the priority of the stacked operator is lower, the stack operator is buffered.
                    while (!stack.isEmpty()) {
                        char c = stack.getFirst();
                        if (c == '*' || c == '/') {
                            resultBuilder.append(stack.removeFirst());
                        } else {
                            break;
                        }
                    }
                    stack.addFirst(token);
                    break;
                case '*':
                case '/':
                case '(':
                    stack.addFirst(token);
                    break;
                case ')':
                    // 「(From ")Operators up to "to buffer"
                    List<Object> list = Arrays.asList(stack.toArray());
                    int index = list.indexOf('(');

                    Deque<Character> workStack = new ArrayDeque<>();
                    for (int i = 0; i <= index; i++) {
                        char c = stack.removeFirst();
                        if (c != '(') {
                            workStack.addFirst(c);
                        }
                    }

                    while (!workStack.isEmpty()) {
                        resultBuilder.append(workStack.removeFirst());
                    }
                    break;
                default:
                    //In the case of numerical value
                    resultBuilder.append(token);
                    break;
            }
        }

        while (!stack.isEmpty()) {
            resultBuilder.append(stack.removeFirst());
        }
        return resultBuilder.toString();
    }
}

At the end

Please let me know if there is a bug. If there are no bugs, please use it (laughs) Thanks to the internet for getting the information you want to know with the quoter.