Basic Calculator II LeetCode solution in C++

1
class Solution {
2
 public:
3
  int calculate(string s) {
4
    stack<int> nums;
5
    stack<char> ops;
6
    int n = 0;
7
    for (int i = 0; i < s.size(); ++i) {
8
      if (s[i] >= '0' && s[i] <= '9') {
9
        string t(1, s[i]);
10
        n = n * 10 + stoi(t);
11
      } else if (s[i] == '+' || s[i] == '-' || s[i] == '*' || s[i] == '/') {
12
        nums.push(n);
13
        n = 0;
14
        if (!ops.empty() && (ops.top() == '*' || ops.top() == '/')) {
15
          int n2 = nums.top();
16
          nums.pop();
17
          int n1 = nums.top();
18
          nums.pop();
19
          if (ops.top() == '*')
20
            nums.push(n1 * n2);
21
          else
22
            nums.push(n1 / n2);
23
          ops.pop();
24
        }
25
        ops.push(s[i]);
26
      }
27
    }
28
    nums.push(n);
29
    if (!ops.empty() && (ops.top() == '*' || ops.top() == '/')) {
30
      int n2 = nums.top();
31
      nums.pop();
32
      int n1 = nums.top();
33
      nums.pop();
34
      if (ops.top() == '*')
35
        nums.push(n1 * n2);
36
      else
37
        nums.push(n1 / n2);
38
      ops.pop();
39
    }
40
    stack<int> tnums;
41
    stack<char> tops;
42
    while (!nums.empty()) {
43
      tnums.push(nums.top());
44
      nums.pop();
45
    }
46
    while (!ops.empty()) {
47
      tops.push(ops.top());
48
      ops.pop();
49
    }
50

51
    while (!tops.empty()) { // cout<<tops.top()<<" " ;
52
      int n1 = tnums.top();
53
      tnums.pop();
54
      int n2 = tnums.top();
55
      tnums.pop();
56
      if (tops.top() == '+')
57
        tnums.push(n1 + n2);
58
      else
59
        tnums.push(n1 - n2);
60
      tops.pop();
61
    }
62
    return tnums.top();
63
  }
64
};