题目：

题解：

class Solution {public int calculate(String s) {Deque<Integer> ops = new LinkedList<Integer>();ops.push(1);int sign = 1;int ret = 0;int n = s.length();int i = 0;while (i < n) {if (s.charAt(i) == ' ') {i++;} else if (s.charAt(i) == '+') {sign = ops.peek();i++;} else if (s.charAt(i) == '-') {sign = -ops.peek();i++;} else if (s.charAt(i) == '(') {ops.push(sign);i++;} else if (s.charAt(i) == ')') {ops.pop();i++;} else {long num = 0;while (i < n && Character.isDigit(s.charAt(i))) {num = num * 10 + s.charAt(i) - '0';i++;}ret += sign * num;}}return ret;}
}