将中缀表达式转换为后缀表达式（逆波兰表达式）

看Java的栈和队列，然后就……写了个转换的Demo（后来发现leetcode上的题是计算后缀表达式的结果，我写了个转换的func就没啥用。

但是好不容易写出来了，删掉又觉得可惜，遂放在这里做一个记录。

public static void main(String[] args) {
        String result = changeMedialExpressions();
        System.out.println(result);
    }

    private static String changeMedialExpressions() {
        String medialExpressions = "(5+4)*3-2";
        String[] strMedialExpressions = medialExpressions.split("");
        //改成后缀表达式（逆波兰表达式）
        Stack stringStack = new Stack<>(); //数字
        Stack symbolsStack = new Stack<>(); //符号
        for (int i = 0; i < strMedialExpressions.length; i++) {
            List> list = new ArrayList<>();
            switch (strMedialExpressions[i]){
                case "+": //1
                    list = getResult(symbolsStack,stringStack,strMedialExpressions[i],1);
                    break;
                case "-": //2
                    list = getResult(symbolsStack,stringStack,strMedialExpressions[i],2);
                    break;
                case "*": //3
                    list = getResult(symbolsStack,stringStack,strMedialExpressions[i],3);
                    break;
                case "/": //4
                    list = getResult(symbolsStack,stringStack,strMedialExpressions[i],4);
                    break;
                case "(": //5
                    list = getResult(symbolsStack,stringStack,strMedialExpressions[i],5);
                    break;
                case ")": //6
                    list = getResult(symbolsStack,stringStack,strMedialExpressions[i],6);
                    break;
                default:
                    stringStack.push(strMedialExpressions[i]); //如果是数字就直接扔进去
                    list.add(symbolsStack);
                    list.add(stringStack);
                    break;
            }
            symbolsStack = list.get(0);
            stringStack = list.get(1);

        }

        String result = "";
        for (int i = 0; i < stringStack.size(); i++) {
            /*System.out.print(stringStack.get(i));*/
            result+=stringStack.get(i);
        }

        for (int i = symbolsStack.size()-1; i >=0; i--) {
            //System.out.print(symbolsStack.get(i));
            result+=symbolsStack.get(i);
        }
        return result;
    }

    /*
    抽调方法
     */
    private static List> getResult(Stack symbolsStack, Stack stringStack, String strMedialExpression, int num) {
        List> list = new ArrayList<>();
        if(symbolsStack.isEmpty()){
            symbolsStack.push(strMedialExpression);
            list.add(symbolsStack);
            list.add(stringStack);
        }else{
            //判断优先级
            list = checkPriority(symbolsStack,stringStack,strMedialExpression,num);
        }
        return list;
    }

    /*
    检查优先级
     */
    private static List> checkPriority(Stack symbolsStack, Stack stringStack
                                                ,String symbols,int priority) {
        List> list = new ArrayList<>();
        if(priority == 5 || priority == 4 || priority == 3){ //如果是( * /就直接扔进去
            symbolsStack.push(symbols);
        }
        if(priority == 1 || priority == 2){ //+ 和 - 要进行遍历
            if(symbolsStack.peek().equals("+") || symbolsStack.peek().equals("-") || symbolsStack.peek().equals("(")){ //如果栈顶元素是 + - ( 就直接扔进去
                symbolsStack.push(symbols);
            }else{ //如果是 * 或者 /就要 进行插入
                List list1 = getSymbolsStack(symbolsStack,symbols,stringStack);
                symbolsStack = list1.get(0);
                stringStack = list1.get(1);
            }
        }
        if(priority == 6){ //)要连着d出。直到）为止,放入stringStack
            //不能一起return 就写在这里
            String a = symbolsStack.peek();
            while(!a.equals("(")){
                stringStack.push(a);
                symbolsStack.pop();
                a = symbolsStack.peek();
            }
            symbolsStack.pop();
        }
        list.add(symbolsStack);
        list.add(stringStack);
        return list;
    }

    /*
    插入符号
     */
    private static List getSymbolsStack(Stack symbolsStack,String symbols,Stack stringStack) {
        int num = 0;
        if(symbolsStack.isEmpty()){
            symbolsStack.push(symbols);
        }else{
            for (int i = symbolsStack.size()-1; i >=0 ; i--) {
                if(symbolsStack.get(i).equals(symbols) || symbolsStack.get(i).equals("+") || symbolsStack.get(i).equals("-")){ //找到了
                    num = i;
                    break;
                }else{
                    continue;
                }
            }
            //记下num，然后push
            for (int i = symbolsStack.size()-1;i >= num;i--) {
                stringStack.push(symbolsStack.peek());
                symbolsStack.pop();
            }
            symbolsStack.push(symbols);
        }
        List list = new ArrayList<>();
        list.add(symbolsStack);
        list.add(stringStack);
        return list;
    }