基本计数器II

题目

思路

• 乘除先运算、减法就将数变为负数，最后所有数相加

  代码

  class Solution {
    public int calculate(String s) {
        char[] chars = s.toCharArray();
        int len = chars.length;
        Stack<Integer> nums = new Stack<>();
        char sign = '+';
        int num = 0;
        for (int i = 0; i < len; i++) {
            if (chars[i] >= '0') {
                num = num * 10 + (chars[i] - '0');
            } 
            if (chars[i] < '0' && chars[i] != ' ' || i == len - 1) {
                if (sign == '+') {
                    nums.push(num);
                } else if (sign == '-') {
                    nums.push(-num);
                } else if (sign == '*' || sign == '/'){
                    int m = sign == '*' ? nums.pop() * num : nums.pop() / num;
                    nums.push(m);
                }
                sign = chars[i];
                num = 0;
            }
        }
        int res = 0;
        while (nums.size() != 0) {
            res += nums.pop();
        }
        return res;
    }
  }

  基本计数器II