医学图像分类

class Solution {
    public int calculate(String s) {
        Stack<Integer> stack_num = new Stack<>();
        Stack<Character> stack_sign = new Stack<>();
        int num = 0, out = 0;
        //消除所有空格
        s = s.replaceAll(" ","");
        //反正第一个是负数
        stack_num.push(0);
        for(int i = 0; i < s.length(); i++){
        //先考虑整数
            if(s.charAt(i) >= '0' && s.charAt(i) <= '9') 
            {
                num = 0;
                while(i < s.length() && s.charAt(i) >= '0' && s.charAt(i) <= '9'){
                    num = num * 10 + s.charAt(i) - '0';
                    i++;
                }
                i--;
                stack_num.push(num);
             //再考虑符号
            }else{
            //如果是右括号，则一直运算到左括号
                if(s.charAt(i) == ')'){
                    while(stack_sign.peek() != '('){
                        int y = stack_num.pop();
                        int x = stack_num.pop();
                        if(stack_sign.pop() == '-'){
                            stack_num.push(x-y);
                        }else{
                            stack_num.push(x+y);
                        }
                    }
                    stack_sign.pop();
                }
                //如果是左括号则直接进符号栈
                else if(s.charAt(i) == '(')
                    stack_sign.push('(');
                else{
                //特殊情况就是左括号后第一个字符是正负号
                    if(i > 0 && s.charAt(i-1) == '(')
                        stack_num.push(0);
                    //剩下的就是加减法符号，再进栈之前要先把之前可以进行加减运算的进行计算
                    while(!stack_sign.isEmpty() && stack_sign.peek() != '(' && stack_num.size() >= 2){
                        int y = stack_num.pop();
                        int x = stack_num.pop();
                        if(stack_sign.pop() == '-'){
                            stack_num.push(x-y);
                        }else{
                            stack_num.push(x+y);
                        }
                    }
                    stack_sign.push(s.charAt(i));
                }
            }
        }

        while(!stack_sign.isEmpty()){
            int y = stack_num.pop();
            int x = stack_num.pop();
            if(stack_sign.pop() == '-'){
                stack_num.push(x-y);
            }else{
                stack_num.push(x+y);
            }
        }
        return stack_num.pop();
    }
}