Evaluate Reverse Polish Notation

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problem description

try 1

result:答案正确:恭喜！您提交的程序通过了所有的测试用例
code:

import java.util.*;
public class Solution {
     /**the program need a stack.
     * Generally, we should convert a String tokens into a char[].
     * But in this chanllenge,tokens is a "char[]",so we don't nee a char[].
     * Besides,we should use Integer.paraseInt() to convert a char to int.
     *if there an exception,it mean the char is a operators.
     */
    public int evalRPN(String[] tokens) {
        Stack<Integer> stack=new Stack<>();
        for(int i=0;i<tokens.length;++i){
            try {
                Integer temp = Integer.parseInt(tokens[i]);
                stack.push(temp);
            }catch (NumberFormatException e){//mean  tokens[i] is a operator
                /*pop out two operand*/
                Integer rightOperand=stack.pop();
                Integer leftOperand=stack.pop();

                if("+".equals(tokens[i])){
                    stack.push(leftOperand+rightOperand);
                }else if("-".equals(tokens[i])){
                    stack.push(leftOperand-rightOperand);
                }else if("*".equals(tokens[i])){
                    stack.push(leftOperand*rightOperand);
                }else if("/".equals(tokens[i])){
                    stack.push(leftOperand/rightOperand);
                }
            }
        }
        
        return stack.pop();
    }
}

Anylze:

Conclusion

1. Integer.parseInt() can convert String to int.And the function can throws NumberFormatException(it is a unchecked exception).