224. 基本计算器

224. 基本计算器

class Solution {
    public int calculate(String s) {
        // 预处理
        s = s.replace(" ", "");
        s = s.replace("(-", "(0-");
        Deque<Integer> num = new LinkedList<>();
        num.push(0);
        Deque<Character> ch = new LinkedList<>();
        int index = 0;
        while (index < s.length()) {
            char cur = s.charAt(index);
            if (cur == '(') {
                ch.push(cur);
            } else if (cur == ')') {
                // 计算直到遇到左边的'('
                while (ch.peek() != '(') {
                    cal(num, ch);
                }
                // 弹出左边的'('
                ch.pop();
            } else if (cur == '+' || cur == '-') {
                if (ch.isEmpty() ||ch.peek() == '(') {
                    ch.push(cur);
                } else {
                    cal(num, ch);
                    ch.push(cur);
                }
            } else {
                int curNum = 0;
                while (index < s.length() && Character.isDigit(s.charAt(index))) {
                    curNum = 10 * curNum + (s.charAt(index) - '0');
                    ++index;
                }
                num.push(curNum);
                continue;
            }
            ++index;
        } 
        while (!ch.isEmpty()) {
            cal(num, ch);
        }
        return num.peek();
    } 
    private void cal(Deque<Integer> num, Deque<Character> ch) {
        int num1 = num.pop();
        int num2 = num.pop();
        if (ch.peek() == '+') {
            num.push(num1 + num2);
        } else {
            num.push(num2 - num1);
        }
        ch.pop();
    }
}