# 0224. Basic Calculator
###### tags: `Leetcode` `Calculator` `Hard`
Link: https://leetcode.com/problems/basic-calculator/
## 思路
和其他calculator一样的写法~
## Code

class Solution {
    public int calculate(String s) {
        s = s.replaceAll(" ","");
        char[] cs = s.toCharArray();
        int len = s.length();
        Stack<Integer> nums = new Stack<>();
        nums.add(0);
        Stack<Character> ops = new Stack<>();
        for(int i = 0;i < len;i++){
            char c = cs[i];
            if(c == '('){
                ops.add('(');
            }
            else if(c == ')'){
                while(!ops.isEmpty()){
                    if(ops.peek()!='('){
                        compute(nums, ops);
                    }
                    else{
                        ops.pop();
                        break;
                    }
                }
            }
            else if(Character.isDigit(c)){
                int num = 0;
                int j = i;
                while(j<len && Character.isDigit(cs[j])){
                    num = num*10 + (cs[j]-'0');
                    j++;
                }
                nums.add(num);
                i = j-1;
            }
            else{
                if(i!=0 && (cs[i-1]=='('||cs[i-1]=='+'||cs[i-1]=='-')){
                    nums.add(0);
                }
                else{
                    while(!ops.isEmpty() && ops.peek()!='('){
                        compute(nums, ops);
                    }
                }
                ops.add(c);
            }
        }
        while(!ops.isEmpty()) compute(nums, ops);
        return nums.peek();
    }
    public void compute(Stack<Integer> nums, Stack<Character> ops){
        int b = nums.pop();
        int a = nums.pop();
        char c = ops.pop();
        if(c=='+') nums.push(a+b);
        if(c=='-') nums.push(a-b);
        
    }
}