leetcode--evaluate-reverse-polish-notation

Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are+,-,*,/. Each operand may be an integer or another expression.

Some examples:

["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9

["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6

分析：逆波兰表达式的计算；
建立一个栈，将每个数字压入栈，当遇到计算符事，弹出前两个数参与计算，并把结果压栈

import java.util.*;
public class Solution {
public int evalRPN(String[] tokens) {
Stack<Integer> stackNum=new Stack<>();
int len=tokens.length;
for(int i=0;i<len;i++){
try{
stackNum.push(Integer.parseInt(tokens[i]));
}catch(Exception e){
String operation=tokens[i];
int numA=stackNum.pop();
int numB=stackNum.pop();
switch(operation){
case "+":
stackNum.push(numB+numA);
break;
case "-":
stackNum.push(numB-numA);
break;
case "*":
stackNum.push(numB*numA);
break;
case "/":
stackNum.push(numB/numA);
break;
}
}
}
return stackNum.pop();
}
}