leetcode:Basic Calculator

写一个支持+-和()的运算表达式的求解，因为题目比较简单，直接穷举计算，没有使用到优先级判断了

import java.util.HashMap;import java.util.Scanner;import java.util.Stack;public class Solution {    public int calculate(String s) {        Stack<Integer> nums = new Stack<Integer>();        Stack<Character> operation = new Stack<Character>();        int num = 0;        //s = "(0+" + s + ")";        s = "(" + s + ")";        char[] ch = s.toCharArray();        for(int i = 0 ; i < ch.length;++i){            char c = ch[i];            if(Character.isDigit(ch[i])){                do{                    num = num * 10 + ch[i++] - '0';                }while(i < ch.length && Character.isDigit(ch[i]));                --i;                nums.push(num);                num = 0;                continue;            }            if(c == ')'){                char topOp = operation.pop();                if(topOp == '('){                    continue;                }                int b = nums.pop();                int a = nums.pop();                nums.push(doOp(a, topOp, b));                operation.pop();            }else if(c == '('){                operation.push(c);            }else if(c == '+' || c == '-'){                char topOp = operation.peek();                if(topOp == '('){                    operation.push(c);                    continue;                }                int a = nums.pop();                int b = nums.pop();                nums.push(doOp(b, topOp, a));                operation.pop();                operation.push(c);            }        }        return nums.pop();    }    public int doOp(int a, char op, int b){        if(op == '-') b = -b;        return a + b;    }    public static void main(String[] args)throws Exception{        String s = "";        Scanner cin = new Scanner(System.in);        Solution solution = new Solution();        while(!s.equals("bye")){            s = cin.nextLine();            int ans = solution.calculate(s);            System.out.println(ans);        }    }}