package Stacks;

import org.junit.Test;

import java.util.Stack;

/**

* @author dekai.kong

* @difficult easy

* @create 2020-07-28 11:34

* @from 计算逆波兰表达式

**/

public class EvalPRN {

public EvalPRN() {

}

public int evalPrn(String[] s){

int ans = 0;

String op = "+-*/";

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

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

if(op.indexOf(s[i])==-1){

stack.push(Integer.parseInt(s[i]));

}else{

int count = 0;

while(!stack.isEmpty() && ++count<2){

int b = stack.pop();

int a = stack.pop();

if(s[i] == "+") stack.push(a+b);

else if(s[i] == "-") stack.push(a-b);

else if(s[i] == "*") stack.push(a*b);

else if(s[i] == "/") stack.push(a/b);

}

}

}

ans = stack.pop();

return ans;

}

@Test

public void test() {

evalPrn(new String[]{"2","3","1","-","4","*","+"});

}

}