中綴表達式轉後綴表達式--java版本 另附思路

首先給出僞代碼

input(expr)
map<K,V> Map
Map.put('(',-1)
Map.put('[+,-]',1)
Map.put('[*,/]',2)
#建立字典映射 

for i in expr:
#遍歷expr中的個體元素
	if i is number:
		string+=number
#如果是數據則直接輸出
	else
		if i is ):
	#如果是右括號，那麼就要開始把符號棧中的元素彈出，直到當前的優先級比我低
	#簡單來說如果只有+-*/四則運算，如果是*號那麼要把* /在符號棧中彈出來，讓他們先去運算
	#如果是+-，則彈出+-*/
			while(stack.peek()!='('):
				string+=stack.pop()
			stack.pop()#扔掉'('
			stack.push(i)
		else:
		
			while(Map[i]>stack.peek()):	
				string+=stack.pop()
				if stack is empty or stack.peek() is '(':
					break
			Stack.push(i)
#如果棧還沒有空，繼續
	while(stack not empty):
		string+=stack.pop()
	return string

再給出java版本的實現

package day05;


import java.util.HashMap;
import java.util.Stack;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * @author 海綿寶寶
 * @create 2019- 10- 29 19:45
 **/
public class Problems {

    public static boolean isNumber(char c){
        String ss = ""+c;
        Pattern pattern=Pattern.compile("[0-9]*");
        return pattern.matcher(ss).matches();
    }
    //中綴表達式轉後綴表達式
    public static String MiddleToBack(String args){
        HashMap<Character, Integer>map = new HashMap<Character, Integer>();
        map.put('(', -1);
        map.put(')', 100);
        map.put('+', 0);
        map.put('-', 0);
        map.put('*', 1);
        map.put('/', 1);

        char[] expr =args.toCharArray();
        Stack<Character>OpStack = new Stack<Character>();
        String string="";
        String backString="";
        for (int i = 0; i < expr.length; i++) {
            if (isNumber(expr[i])){
                while (isNumber(expr[i])){
                    string+=expr[i];
                    i++;
                    if (i==expr.length)break;
                }
                if (i==expr.length);
                else i--;
//
                backString+=string+" ";
                string="";
            }
            else{
                if (expr[i]==' ')continue;
                else{
                    if (OpStack.isEmpty()){
                        OpStack.push(expr[i]);
                    }
                    else{
                        if (expr[i]=='('){
                            OpStack.push(expr[i]);
                        }
                        else if(expr[i]==')'){
                            while (OpStack.isEmpty() == false&&OpStack.peek()!='('){
                                backString+=OpStack.pop()+" ";
                            }
                            if (!OpStack.isEmpty())
                            OpStack.pop();
                        }
                        else {
                            if (OpStack.isEmpty()){
                                OpStack.push(expr[i]);
                            }
                            while (map.get(expr[i])<map.get(OpStack.peek())){
                                if (OpStack.peek()=='(')break;
                                backString+=OpStack.pop()+" ";
                                if (OpStack.isEmpty())break;
                            }
                            OpStack.push(expr[i]);
                        }
                    }
                }
            }
        }
        while (!OpStack.isEmpty()){
            backString+=OpStack.pop()+ " ";
        }
        return backString;
    }


    public static void main(String[] args) {
        String expr= "(5+6)+7";
        System.out.println(MiddleToBack(expr));
    }
}

最後附上處理後綴表達的一半方法

 public static int SolveTheProblem(String expr){

        Stack<Integer>NumStack = new Stack<Integer>();
        String[]exp = expr.split(" ");
        for (String i :
                exp) {
            if (isNumber(i)){
                NumStack.push((Integer.parseInt(i)));
            }
            else{
                int second = NumStack.pop();
                int first=NumStack.pop();
                int result = 0;
                switch (i){
                    case "+":result=second+first;
                        break;
                    case "-":result=first-second;
                        break;
                    case "*":result=first*second;
                        break;
                    case "/":result=first/second;
                        break;
                    default:
                        System.out.println("error,uninvalib simble");
                }
                NumStack.push(result);
            }
        }
        return NumStack.peek();
    }