[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

 

Solution:

public class Solution {    public int evalRPN(String[] tokens) {        if(tokens==null)            return 0;        Stack<Integer> s=new Stack<Integer>();        for(int i=0;i<tokens.length;++i){            if(isNumber(tokens[i])){                s.add(Integer.parseInt(tokens[i]));            }else{                int param_1=s.pop();                int param_2=s.pop();                s.add(calc(param_1,param_2,tokens[i]));            }        }        return s.pop();    }    private int calc(int param_1, int param_2, String op) {        // TODO Auto-generated method stub        switch (op.charAt(0)) {        case ‘+‘:            return param_1+param_2;        case ‘-‘:            return param_2-param_1;        case ‘*‘:            return param_1*param_2;        case ‘/‘:            return param_2/param_1;        default:            return 0;        }    }    private boolean isNumber(String s) {        // TODO Auto-generated method stub        try {            int i_s=Integer.parseInt(s);        } catch (Exception e) {            // TODO: handle exception            return false;        }        return true;    }}

Note:

Determine if it is a number:

 1 private boolean isNumber(String s) { 2         // TODO Auto-generated method stub 3         try { 4             int i_s=Integer.parseInt(s); 5         } catch (Exception e) { 6             // TODO: handle exception 7             return false; 8         } 9         return true;10 }

 

[Leetcode] evaluate reverse Polish notation